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 $205.46   9.171%   $224.3027   $224.30   $224.30   $224.30  
  Purchase #2 $245.74   8.496%   $266.6181   $266.62   $266.60   $266.60  
  Purchase #3 $227.94   4.588%   $238.3979   $238.40   $238.40   $238.40  
  Purchase #4 $60.77   12.380%   $68.2933   $68.29   $68.30   $68.30  
  Purchase #5 $30.49   6.271%   $32.402   $32.40   $32.40   $32.40  
  Purchase #6 $185.76   6.117%   $197.1229   $197.12   $197.10   $197.10  
  Purchase #7 $205.40   3.681%   $212.9608   $212.96   $212.95   $213.00  
  7 purchase totals = $1,161.56       $1,240.0977   $1,240.09   $1,240.05   $1,240.10