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 $87.44   6.732%   $93.3265   $93.33   $93.35   $93.30  
  Purchase #2 $42.68   3.873%   $44.333   $44.33   $44.35   $44.30  
  Purchase #3 $242.90   10.694%   $268.8757   $268.88   $268.90   $268.90  
  Purchase #4 $224.92   8.675%   $244.4318   $244.43   $244.45   $244.40  
  Purchase #5 $241.78   3.132%   $249.3525   $249.35   $249.35   $249.40  
  Purchase #6 $79.76   11.554%   $88.9755   $88.98   $89.00   $89.00  
  Purchase #7 $32.42   11.123%   $36.0261   $36.03   $36.05   $36.00  
  7 purchase totals = $951.90       $1,025.3211   $1,025.33   $1,025.45   $1,025.30