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 $56.37   4.724%   $59.0329   $59.03   $59.05   $59.00  
  Purchase #2 $245.53   7.365%   $263.6133   $263.61   $263.60   $263.60  
  Purchase #3 $119.32   9.609%   $130.7855   $130.79   $130.80   $130.80  
  Purchase #4 $8.66   7.870%   $9.3415   $9.34   $9.35   $9.30  
  Purchase #5 $49.98   5.733%   $52.8454   $52.85   $52.85   $52.80  
  Purchase #6 $198.61   9.434%   $217.3469   $217.35   $217.35   $217.30  
  Purchase #7 $27.82   9.367%   $30.4259   $30.43   $30.45   $30.40  
  7 purchase totals = $706.29       $763.3914   $763.40   $763.45   $763.20