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 $65.54   3.352%   $67.7369   $67.74   $67.75   $67.70  
  Purchase #2 $115.96   3.292%   $119.7774   $119.78   $119.80   $119.80  
  Purchase #3 $208.82   3.212%   $215.5273   $215.53   $215.55   $215.50  
  Purchase #4 $60.43   10.604%   $66.838   $66.84   $66.85   $66.80  
  Purchase #5 $126.39   4.794%   $132.4491   $132.45   $132.45   $132.40  
  Purchase #6 $187.40   12.411%   $210.6582   $210.66   $210.65   $210.70  
  Purchase #7 $199.40   10.691%   $220.7179   $220.72   $220.70   $220.70  
  7 purchase totals = $963.94       $1,033.7048   $1,033.72   $1,033.75   $1,033.60