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 $250.27   10.181%   $275.75   $275.75   $275.75   $275.80  
  Purchase #2 $96.90   8.259%   $104.903   $104.90   $104.90   $104.90  
  Purchase #3 $66.71   9.154%   $72.8166   $72.82   $72.80   $72.80  
  Purchase #4 $157.98   13.251%   $178.9139   $178.91   $178.90   $178.90  
  Purchase #5 $136.61   6.113%   $144.961   $144.96   $144.95   $145.00  
  Purchase #6 $135.74   9.747%   $148.9706   $148.97   $148.95   $149.00  
  Purchase #7 $12.73   13.411%   $14.4372   $14.44   $14.45   $14.40  
  7 purchase totals = $856.94       $940.7523   $940.75   $940.70   $940.80