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 $194.71   4.227%   $202.9404   $202.94   $202.95   $202.90  
  Purchase #2 $211.91   6.664%   $226.0317   $226.03   $226.05   $226.00  
  Purchase #3 $58.97   6.817%   $62.99   $62.99   $63.00   $63.00  
  Purchase #4 $208.27   7.621%   $224.1423   $224.14   $224.15   $224.10  
  Purchase #5 $66.62   8.216%   $72.0935   $72.09   $72.10   $72.10  
  Purchase #6 $59.57   7.248%   $63.8876   $63.89   $63.90   $63.90  
  Purchase #7 $162.69   8.367%   $176.3023   $176.30   $176.30   $176.30  
  7 purchase totals = $962.74       $1,028.3878   $1,028.38   $1,028.45   $1,028.30