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 $68.85   11.223%   $76.577   $76.58   $76.60   $76.60  
  Purchase #2 $52.68   11.738%   $58.8636   $58.86   $58.85   $58.90  
  Purchase #3 $23.88   9.308%   $26.1028   $26.10   $26.10   $26.10  
  Purchase #4 $71.91   5.210%   $75.6565   $75.66   $75.65   $75.70  
  Purchase #5 $207.38   12.872%   $234.074   $234.07   $234.05   $234.10  
  Purchase #6 $171.43   9.518%   $187.7467   $187.75   $187.75   $187.70  
  Purchase #7 $47.88   13.145%   $54.1738   $54.17   $54.15   $54.20  
  7 purchase totals = $644.01       $713.1944   $713.19   $713.15   $713.30