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 $244.39   7.174%   $261.9225   $261.92   $261.90   $261.90  
  Purchase #2 $49.27   9.480%   $53.9408   $53.94   $53.95   $53.90  
  Purchase #3 $26.37   11.218%   $29.3282   $29.33   $29.35   $29.30  
  Purchase #4 $65.34   8.292%   $70.758   $70.76   $70.75   $70.80  
  Purchase #5 $115.91   8.403%   $125.6499   $125.65   $125.65   $125.60  
  Purchase #6 $39.42   13.715%   $44.8265   $44.83   $44.85   $44.80  
  Purchase #7 $157.32   8.567%   $170.7976   $170.80   $170.80   $170.80  
  7 purchase totals = $698.02       $757.2235   $757.23   $757.25   $757.10