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 $59.76   11.213%   $66.4609   $66.46   $66.45   $66.50  
  Purchase #2 $16.54   5.141%   $17.3903   $17.39   $17.40   $17.40  
  Purchase #3 $41.53   11.593%   $46.3446   $46.34   $46.35   $46.30  
  Purchase #4 $103.65   8.519%   $112.4799   $112.48   $112.50   $112.50  
  Purchase #5 $196.85   3.773%   $204.2772   $204.28   $204.30   $204.30  
  Purchase #6 $168.28   9.602%   $184.4382   $184.44   $184.45   $184.40  
  Purchase #7 $118.99   10.736%   $131.7648   $131.76   $131.75   $131.80  
  7 purchase totals = $705.60       $763.1559   $763.15   $763.20   $763.20