Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $94.92   4.110%   $98.8212   $98.82   $98.80   $98.80  
  Purchase #2 $229.59   13.861%   $261.4135   $261.41   $261.40   $261.40  
  Purchase #3 $205.95   7.654%   $221.7134   $221.71   $221.70   $221.70  
  Purchase #4 $248.51   3.638%   $257.5508   $257.55   $257.55   $257.60  
  Purchase #5 $77.71   12.332%   $87.2932   $87.29   $87.30   $87.30  
  Purchase #6 $207.60   6.831%   $221.7812   $221.78   $221.80   $221.80  
  Purchase #7 $180.33   4.361%   $188.1942   $188.19   $188.20   $188.20  
  7 purchase totals = $1,244.61       $1,336.7675   $1,336.75   $1,336.75   $1,336.80