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 $118.88   5.621%   $125.5622   $125.56   $125.55   $125.60  
  Purchase #2 $6.90   4.314%   $7.1977   $7.20   $7.20   $7.20  
  Purchase #3 $40.53   9.257%   $44.2819   $44.28   $44.30   $44.30  
  Purchase #4 $30.65   5.615%   $32.371   $32.37   $32.35   $32.40  
  Purchase #5 $89.83   13.826%   $102.2499   $102.25   $102.25   $102.20  
  Purchase #6 $37.25   11.407%   $41.4991   $41.50   $41.50   $41.50  
  Purchase #7 $222.86   6.163%   $236.5949   $236.59   $236.60   $236.60  
  7 purchase totals = $546.90       $589.7567   $589.75   $589.75   $589.80