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 $53.82   9.346%   $58.85   $58.85   $58.85   $58.90  
  Purchase #2 $159.84   5.803%   $169.1155   $169.12   $169.10   $169.10  
  Purchase #3 $14.56   6.449%   $15.499   $15.50   $15.50   $15.50  
  Purchase #4 $154.42   3.298%   $159.5128   $159.51   $159.50   $159.50  
  Purchase #5 $223.64   5.733%   $236.4613   $236.46   $236.45   $236.50  
  Purchase #6 $229.28   13.788%   $260.8931   $260.89   $260.90   $260.90  
  Purchase #7 $121.89   8.330%   $132.0434   $132.04   $132.05   $132.00  
  7 purchase totals = $957.45       $1,032.3751   $1,032.37   $1,032.35   $1,032.40