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 $247.82   5.557%   $261.5914   $261.59   $261.60   $261.60  
  Purchase #2 $51.27   3.401%   $53.0137   $53.01   $53.00   $53.00  
  Purchase #3 $157.99   5.319%   $166.3935   $166.39   $166.40   $166.40  
  Purchase #4 $53.93   12.741%   $60.8012   $60.80   $60.80   $60.80  
  Purchase #5 $14.88   10.497%   $16.442   $16.44   $16.45   $16.40  
  Purchase #6 $8.65   9.802%   $9.4979   $9.50   $9.50   $9.50  
  Purchase #7 $185.63   5.165%   $195.2178   $195.22   $195.20   $195.20  
  7 purchase totals = $720.17       $762.9575   $762.95   $762.95   $762.90