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 $35.45   6.241%   $37.6624   $37.66   $37.65   $37.70  
  Purchase #2 $112.61   11.272%   $125.3034   $125.30   $125.30   $125.30  
  Purchase #3 $13.49   11.348%   $15.0208   $15.02   $15.00   $15.00  
  Purchase #4 $243.62   7.591%   $262.1132   $262.11   $262.10   $262.10  
  Purchase #5 $229.88   7.855%   $247.9371   $247.94   $247.95   $247.90  
  Purchase #6 $195.98   7.648%   $210.9686   $210.97   $210.95   $211.00  
  Purchase #7 $130.69   5.241%   $137.5395   $137.54   $137.55   $137.50  
  7 purchase totals = $961.72       $1,036.5450   $1,036.54   $1,036.50   $1,036.50