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 $64.58   3.533%   $66.8616   $66.86   $66.85   $66.90  
  Purchase #2 $246.42   12.170%   $276.4093   $276.41   $276.40   $276.40  
  Purchase #3 $85.70   13.372%   $97.1598   $97.16   $97.15   $97.20  
  Purchase #4 $34.94   9.733%   $38.3407   $38.34   $38.35   $38.30  
  Purchase #5 $130.26   13.540%   $147.8972   $147.90   $147.90   $147.90  
  Purchase #6 $91.73   3.536%   $94.9736   $94.97   $94.95   $95.00  
  Purchase #7 $225.65   4.867%   $236.6324   $236.63   $236.65   $236.60  
  7 purchase totals = $879.28       $958.2746   $958.27   $958.25   $958.30