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 $246.50   3.840%   $255.9656   $255.97   $255.95   $256.00  
  Purchase #2 $59.83   4.693%   $62.6378   $62.64   $62.65   $62.60  
  Purchase #3 $84.68   11.234%   $94.193   $94.19   $94.20   $94.20  
  Purchase #4 $139.97   9.600%   $153.4071   $153.41   $153.40   $153.40  
  Purchase #5 $162.26   8.800%   $176.5389   $176.54   $176.55   $176.50  
  Purchase #6 $127.89   8.282%   $138.4818   $138.48   $138.50   $138.50  
  Purchase #7 $115.91   4.750%   $121.4157   $121.42   $121.40   $121.40  
  7 purchase totals = $937.04       $1,002.6399   $1,002.65   $1,002.65   $1,002.60