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 $218.99   11.708%   $244.6293   $244.63   $244.65   $244.60  
  Purchase #2 $176.34   11.330%   $196.3193   $196.32   $196.30   $196.30  
  Purchase #3 $162.94   11.793%   $182.1555   $182.16   $182.15   $182.20  
  Purchase #4 $168.84   13.336%   $191.3565   $191.36   $191.35   $191.40  
  Purchase #5 $194.45   6.293%   $206.6867   $206.69   $206.70   $206.70  
  Purchase #6 $165.26   5.757%   $174.774   $174.77   $174.75   $174.80  
  Purchase #7 $22.34   9.428%   $24.4462   $24.45   $24.45   $24.40  
  7 purchase totals = $1,109.16       $1,220.3675   $1,220.38   $1,220.35   $1,220.40