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 $69.62   5.825%   $73.6754   $73.68   $73.70   $73.70  
  Purchase #2 $151.38   9.663%   $166.0078   $166.01   $166.00   $166.00  
  Purchase #3 $130.76   12.433%   $147.0174   $147.02   $147.00   $147.00  
  Purchase #4 $234.61   11.560%   $261.7309   $261.73   $261.75   $261.70  
  Purchase #5 $91.54   5.703%   $96.7605   $96.76   $96.75   $96.80  
  Purchase #6 $35.64   4.193%   $37.1344   $37.13   $37.15   $37.10  
  Purchase #7 $93.49   11.379%   $104.1282   $104.13   $104.15   $104.10  
  7 purchase totals = $807.04       $886.4546   $886.46   $886.50   $886.40