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 $144.98   12.494%   $163.0938   $163.09   $163.10   $163.10  
  Purchase #2 $108.85   12.452%   $122.404   $122.40   $122.40   $122.40  
  Purchase #3 $138.37   8.482%   $150.1065   $150.11   $150.10   $150.10  
  Purchase #4 $142.99   4.579%   $149.5375   $149.54   $149.55   $149.50  
  Purchase #5 $101.64   10.432%   $112.2431   $112.24   $112.25   $112.20  
  Purchase #6 $6.63   7.824%   $7.1487   $7.15   $7.15   $7.10  
  Purchase #7 $95.82   7.262%   $102.7784   $102.78   $102.80   $102.80  
  7 purchase totals = $739.28       $807.3120   $807.31   $807.35   $807.20