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 $208.75   7.869%   $225.1765   $225.18   $225.20   $225.20  
  Purchase #2 $188.99   8.831%   $205.6797   $205.68   $205.70   $205.70  
  Purchase #3 $209.75   3.708%   $217.5275   $217.53   $217.55   $217.50  
  Purchase #4 $196.97   13.852%   $224.2543   $224.25   $224.25   $224.30  
  Purchase #5 $34.70   8.762%   $37.7404   $37.74   $37.75   $37.70  
  Purchase #6 $234.54   4.218%   $244.4329   $244.43   $244.45   $244.40  
  Purchase #7 $107.40   12.568%   $120.898   $120.90   $120.90   $120.90  
  7 purchase totals = $1,181.10       $1,275.7093   $1,275.71   $1,275.80   $1,275.70