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 $157.95   9.506%   $172.9647   $172.96   $172.95   $173.00  
  Purchase #2 $16.78   9.405%   $18.3582   $18.36   $18.35   $18.40  
  Purchase #3 $53.50   6.586%   $57.0235   $57.02   $57.00   $57.00  
  Purchase #4 $60.32   7.103%   $64.6045   $64.60   $64.60   $64.60  
  Purchase #5 $171.31   5.256%   $180.3141   $180.31   $180.30   $180.30  
  Purchase #6 $234.74   11.568%   $261.8947   $261.89   $261.90   $261.90  
  Purchase #7 $115.64   11.852%   $129.3457   $129.35   $129.35   $129.30  
  7 purchase totals = $810.24       $884.5054   $884.49   $884.45   $884.50