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 $101.84   11.215%   $113.2614   $113.26   $113.25   $113.30  
  Purchase #2 $129.37   5.868%   $136.9614   $136.96   $136.95   $137.00  
  Purchase #3 $166.63   4.459%   $174.06   $174.06   $174.05   $174.10  
  Purchase #4 $32.33   4.431%   $33.7625   $33.76   $33.75   $33.80  
  Purchase #5 $24.96   9.769%   $27.3983   $27.40   $27.40   $27.40  
  Purchase #6 $136.30   3.782%   $141.4549   $141.45   $141.45   $141.50  
  Purchase #7 $68.52   7.202%   $73.4548   $73.45   $73.45   $73.50  
  7 purchase totals = $659.95       $700.3533   $700.34   $700.30   $700.60