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 $67.40   11.424%   $75.0998   $75.10   $75.10   $75.10  
  Purchase #2 $55.68   10.170%   $61.3427   $61.34   $61.35   $61.30  
  Purchase #3 $185.31   8.635%   $201.3115   $201.31   $201.30   $201.30  
  Purchase #4 $127.98   8.128%   $138.3822   $138.38   $138.40   $138.40  
  Purchase #5 $86.64   12.396%   $97.3799   $97.38   $97.40   $97.40  
  Purchase #6 $123.94   8.314%   $134.2444   $134.24   $134.25   $134.20  
  Purchase #7 $229.97   7.107%   $246.314   $246.31   $246.30   $246.30  
  7 purchase totals = $876.92       $954.0745   $954.06   $954.10   $954.00