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 $40.33   13.748%   $45.8746   $45.87   $45.85   $45.90  
  Purchase #2 $132.45   3.797%   $137.4791   $137.48   $137.50   $137.50  
  Purchase #3 $218.56   4.808%   $229.0684   $229.07   $229.05   $229.10  
  Purchase #4 $22.56   11.137%   $25.0725   $25.07   $25.05   $25.10  
  Purchase #5 $55.48   12.405%   $62.3623   $62.36   $62.35   $62.40  
  Purchase #6 $149.67   8.189%   $161.9265   $161.93   $161.95   $161.90  
  Purchase #7 $16.61   9.493%   $18.1868   $18.19   $18.20   $18.20  
  7 purchase totals = $635.66       $679.9702   $679.97   $679.95   $680.10