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 $60.34   9.541%   $66.097   $66.10   $66.10   $66.10  
  Purchase #2 $98.61   6.310%   $104.8323   $104.83   $104.85   $104.80  
  Purchase #3 $15.92   10.309%   $17.5612   $17.56   $17.55   $17.60  
  Purchase #4 $45.70   11.127%   $50.785   $50.79   $50.80   $50.80  
  Purchase #5 $120.96   4.829%   $126.8012   $126.80   $126.80   $126.80  
  Purchase #6 $233.34   5.290%   $245.6837   $245.68   $245.70   $245.70  
  Purchase #7 $242.62   7.471%   $260.7461   $260.75   $260.75   $260.70  
  7 purchase totals = $817.49       $872.5065   $872.51   $872.55   $872.50