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 $229.69   9.678%   $251.9194   $251.92   $251.90   $251.90  
  Purchase #2 $242.98   9.190%   $265.3099   $265.31   $265.30   $265.30  
  Purchase #3 $93.92   11.874%   $105.0721   $105.07   $105.05   $105.10  
  Purchase #4 $168.89   11.483%   $188.2836   $188.28   $188.30   $188.30  
  Purchase #5 $194.95   13.784%   $221.8219   $221.82   $221.80   $221.80  
  Purchase #6 $213.94   13.321%   $242.4389   $242.44   $242.45   $242.40  
  Purchase #7 $62.97   5.528%   $66.451   $66.45   $66.45   $66.50  
  7 purchase totals = $1,207.34       $1,341.2968   $1,341.29   $1,341.25   $1,341.30