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 $232.28   8.172%   $251.2619   $251.26   $251.25   $251.30  
  Purchase #2 $195.55   3.285%   $201.9738   $201.97   $201.95   $202.00  
  Purchase #3 $201.29   11.653%   $224.7463   $224.75   $224.75   $224.70  
  Purchase #4 $136.54   4.335%   $142.459   $142.46   $142.45   $142.50  
  Purchase #5 $166.74   9.468%   $182.5269   $182.53   $182.55   $182.50  
  Purchase #6 $237.45   5.346%   $250.1441   $250.14   $250.15   $250.10  
  Purchase #7 $184.62   12.308%   $207.343   $207.34   $207.35   $207.30  
  7 purchase totals = $1,354.47       $1,460.4550   $1,460.45   $1,460.45   $1,460.40