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 $84.83   10.721%   $93.9246   $93.92   $93.90   $93.90  
  Purchase #2 $7.62   8.732%   $8.2854   $8.29   $8.30   $8.30  
  Purchase #3 $185.70   10.842%   $205.8336   $205.83   $205.85   $205.80  
  Purchase #4 $207.92   4.122%   $216.4905   $216.49   $216.50   $216.50  
  Purchase #5 $123.96   6.754%   $132.3323   $132.33   $132.35   $132.30  
  Purchase #6 $154.30   8.183%   $166.9264   $166.93   $166.95   $166.90  
  Purchase #7 $160.51   10.107%   $176.7327   $176.73   $176.75   $176.70  
  7 purchase totals = $924.84       $1,000.5255   $1,000.52   $1,000.60   $1,000.40