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 $205.37   8.744%   $223.3276   $223.33   $223.35   $223.30  
  Purchase #2 $58.68   10.675%   $64.9441   $64.94   $64.95   $64.90  
  Purchase #3 $24.53   9.783%   $26.9298   $26.93   $26.95   $26.90  
  Purchase #4 $247.55   5.650%   $261.5366   $261.54   $261.55   $261.50  
  Purchase #5 $170.99   10.621%   $189.1508   $189.15   $189.15   $189.20  
  Purchase #6 $34.77   6.589%   $37.061   $37.06   $37.05   $37.10  
  Purchase #7 $137.64   7.794%   $148.3677   $148.37   $148.35   $148.40  
  7 purchase totals = $879.53       $951.3176   $951.32   $951.35   $951.30