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 $206.86   8.765%   $224.9913   $224.99   $225.00   $225.00  
  Purchase #2 $93.85   3.667%   $97.2915   $97.29   $97.30   $97.30  
  Purchase #3 $6.89   10.612%   $7.6212   $7.62   $7.60   $7.60  
  Purchase #4 $139.67   9.789%   $153.3423   $153.34   $153.35   $153.30  
  Purchase #5 $212.92   9.753%   $233.6861   $233.69   $233.70   $233.70  
  Purchase #6 $29.98   9.673%   $32.88   $32.88   $32.90   $32.90  
  Purchase #7 $163.88   12.688%   $184.6731   $184.67   $184.65   $184.70  
  7 purchase totals = $854.05       $934.4855   $934.48   $934.50   $934.50