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 $67.85   12.648%   $76.4317   $76.43   $76.45   $76.40  
  Purchase #2 $163.78   12.315%   $183.9495   $183.95   $183.95   $183.90  
  Purchase #3 $124.61   4.634%   $130.3844   $130.38   $130.40   $130.40  
  Purchase #4 $136.80   9.475%   $149.7618   $149.76   $149.75   $149.80  
  Purchase #5 $53.61   4.669%   $56.1131   $56.11   $56.10   $56.10  
  Purchase #6 $24.65   11.362%   $27.4507   $27.45   $27.45   $27.50  
  Purchase #7 $87.47   7.734%   $94.2349   $94.23   $94.25   $94.20  
  7 purchase totals = $658.77       $718.3261   $718.31   $718.35   $718.30