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 $58.27   3.563%   $60.3462   $60.35   $60.35   $60.30  
  Purchase #2 $149.39   11.186%   $166.1008   $166.10   $166.10   $166.10  
  Purchase #3 $146.59   11.440%   $163.3599   $163.36   $163.35   $163.40  
  Purchase #4 $227.53   7.634%   $244.8996   $244.90   $244.90   $244.90  
  Purchase #5 $185.76   11.591%   $207.2914   $207.29   $207.30   $207.30  
  Purchase #6 $70.82   3.757%   $73.4807   $73.48   $73.50   $73.50  
  Purchase #7 $76.33   7.335%   $81.9288   $81.93   $81.95   $81.90  
  7 purchase totals = $914.69       $997.4074   $997.41   $997.45   $997.40