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 $89.58   9.681%   $98.2522   $98.25   $98.25   $98.30  
  Purchase #2 $199.47   6.703%   $212.8405   $212.84   $212.85   $212.80  
  Purchase #3 $106.43   8.773%   $115.7671   $115.77   $115.75   $115.80  
  Purchase #4 $197.42   13.468%   $224.0085   $224.01   $224.00   $224.00  
  Purchase #5 $146.76   11.662%   $163.8752   $163.88   $163.90   $163.90  
  Purchase #6 $232.53   10.488%   $256.9177   $256.92   $256.90   $256.90  
  Purchase #7 $185.75   5.744%   $196.4195   $196.42   $196.40   $196.40  
  7 purchase totals = $1,157.94       $1,268.0807   $1,268.09   $1,268.05   $1,268.10