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 $94.66   13.605%   $107.5385   $107.54   $107.55   $107.50  
  Purchase #2 $136.92   5.314%   $144.1959   $144.20   $144.20   $144.20  
  Purchase #3 $46.32   4.596%   $48.4489   $48.45   $48.45   $48.40  
  Purchase #4 $93.77   4.452%   $97.9446   $97.94   $97.95   $97.90  
  Purchase #5 $136.92   7.395%   $147.0452   $147.05   $147.05   $147.00  
  Purchase #6 $137.39   5.154%   $144.4711   $144.47   $144.45   $144.50  
  Purchase #7 $116.86   8.289%   $126.5465   $126.55   $126.55   $126.50  
  7 purchase totals = $762.84       $816.1907   $816.20   $816.20   $816.00