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 $22.51   6.768%   $24.0335   $24.03   $24.05   $24.00  
  Purchase #2 $240.29   4.299%   $250.6201   $250.62   $250.60   $250.60  
  Purchase #3 $117.56   7.170%   $125.9891   $125.99   $126.00   $126.00  
  Purchase #4 $41.97   7.806%   $45.2462   $45.25   $45.25   $45.20  
  Purchase #5 $233.94   9.564%   $256.314   $256.31   $256.30   $256.30  
  Purchase #6 $96.34   6.178%   $102.2919   $102.29   $102.30   $102.30  
  Purchase #7 $179.63   4.424%   $187.5768   $187.58   $187.60   $187.60  
  7 purchase totals = $932.24       $992.0716   $992.07   $992.10   $992.00