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 $35.39   3.785%   $36.7295   $36.73   $36.75   $36.70  
  Purchase #2 $241.83   5.521%   $255.1814   $255.18   $255.20   $255.20  
  Purchase #3 $129.36   6.240%   $137.4321   $137.43   $137.45   $137.40  
  Purchase #4 $208.52   5.407%   $219.7947   $219.79   $219.80   $219.80  
  Purchase #5 $45.47   11.616%   $50.7518   $50.75   $50.75   $50.80  
  Purchase #6 $250.94   4.648%   $262.6037   $262.60   $262.60   $262.60  
  Purchase #7 $66.63   5.329%   $70.1807   $70.18   $70.20   $70.20  
  7 purchase totals = $978.14       $1,032.6739   $1,032.66   $1,032.75   $1,032.70