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 $57.29   4.802%   $60.0411   $60.04   $60.05   $60.00  
  Purchase #2 $91.64   6.120%   $97.2484   $97.25   $97.25   $97.20  
  Purchase #3 $124.94   3.745%   $129.619   $129.62   $129.60   $129.60  
  Purchase #4 $84.91   4.229%   $88.5008   $88.50   $88.50   $88.50  
  Purchase #5 $79.93   13.377%   $90.6222   $90.62   $90.60   $90.60  
  Purchase #6 $249.44   12.281%   $280.0737   $280.07   $280.05   $280.10  
  Purchase #7 $234.85   11.419%   $261.6675   $261.67   $261.65   $261.70  
  7 purchase totals = $923.00       $1,007.7727   $1,007.77   $1,007.70   $1,007.70