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 $194.51   4.319%   $202.9109   $202.91   $202.90   $202.90  
  Purchase #2 $212.99   7.772%   $229.5436   $229.54   $229.55   $229.50  
  Purchase #3 $60.38   10.430%   $66.6776   $66.68   $66.70   $66.70  
  Purchase #4 $156.80   9.227%   $171.2679   $171.27   $171.25   $171.30  
  Purchase #5 $92.87   5.643%   $98.1107   $98.11   $98.10   $98.10  
  Purchase #6 $68.68   11.839%   $76.811   $76.81   $76.80   $76.80  
  Purchase #7 $166.74   4.468%   $174.1899   $174.19   $174.20   $174.20  
  7 purchase totals = $952.97       $1,019.5116   $1,019.51   $1,019.50   $1,019.50