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 $50.48   7.667%   $54.3503   $54.35   $54.35   $54.40  
  Purchase #2 $236.69   12.786%   $266.9532   $266.95   $266.95   $267.00  
  Purchase #3 $41.41   12.292%   $46.5001   $46.50   $46.50   $46.50  
  Purchase #4 $87.46   4.195%   $91.1289   $91.13   $91.15   $91.10  
  Purchase #5 $173.79   12.481%   $195.4807   $195.48   $195.50   $195.50  
  Purchase #6 $84.71   10.869%   $93.9171   $93.92   $93.90   $93.90  
  Purchase #7 $39.48   11.149%   $43.8816   $43.88   $43.90   $43.90  
  7 purchase totals = $714.02       $792.2119   $792.21   $792.25   $792.30