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 $85.34   10.335%   $94.1599   $94.16   $94.15   $94.20  
  Purchase #2 $229.43   11.227%   $255.1881   $255.19   $255.20   $255.20  
  Purchase #3 $209.26   5.856%   $221.5143   $221.51   $221.50   $221.50  
  Purchase #4 $43.62   9.359%   $47.7024   $47.70   $47.70   $47.70  
  Purchase #5 $213.44   4.644%   $223.3522   $223.35   $223.35   $223.40  
  Purchase #6 $168.70   4.249%   $175.8681   $175.87   $175.85   $175.90  
  Purchase #7 $27.48   3.320%   $28.3923   $28.39   $28.40   $28.40  
  7 purchase totals = $977.27       $1,046.1773   $1,046.17   $1,046.15   $1,046.30