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 $197.51   4.614%   $206.6231   $206.62   $206.60   $206.60  
  Purchase #2 $95.53   9.540%   $104.6436   $104.64   $104.65   $104.60  
  Purchase #3 $238.77   8.547%   $259.1777   $259.18   $259.20   $259.20  
  Purchase #4 $55.57   3.381%   $57.4488   $57.45   $57.45   $57.40  
  Purchase #5 $86.75   8.468%   $94.096   $94.10   $94.10   $94.10  
  Purchase #6 $193.29   4.872%   $202.7071   $202.71   $202.70   $202.70  
  Purchase #7 $81.92   12.343%   $92.0314   $92.03   $92.05   $92.00  
  7 purchase totals = $949.34       $1,016.7277   $1,016.73   $1,016.75   $1,016.60