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 $57.46   6.622%   $61.265   $61.27   $61.25   $61.30  
  Purchase #2 $24.56   13.870%   $27.9665   $27.97   $27.95   $28.00  
  Purchase #3 $63.50   8.781%   $69.0759   $69.08   $69.10   $69.10  
  Purchase #4 $178.72   11.862%   $199.9198   $199.92   $199.90   $199.90  
  Purchase #5 $118.69   12.152%   $133.1132   $133.11   $133.10   $133.10  
  Purchase #6 $213.81   10.106%   $235.4176   $235.42   $235.40   $235.40  
  Purchase #7 $135.52   5.619%   $143.1349   $143.13   $143.15   $143.10  
  7 purchase totals = $792.26       $869.8929   $869.90   $869.85   $869.90