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 $118.25   13.780%   $134.5449   $134.54   $134.55   $134.50  
  Purchase #2 $182.92   6.804%   $195.3659   $195.37   $195.35   $195.40  
  Purchase #3 $174.31   11.261%   $193.939   $193.94   $193.95   $193.90  
  Purchase #4 $62.28   10.182%   $68.6213   $68.62   $68.60   $68.60  
  Purchase #5 $48.53   4.307%   $50.6202   $50.62   $50.60   $50.60  
  Purchase #6 $149.77   3.744%   $155.3774   $155.38   $155.40   $155.40  
  Purchase #7 $19.50   10.513%   $21.55   $21.55   $21.55   $21.60  
  7 purchase totals = $755.56       $820.0187   $820.02   $820.00   $820.00