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 $64.28   6.193%   $68.2609   $68.26   $68.25   $68.30  
  Purchase #2 $164.79   9.820%   $180.9724   $180.97   $180.95   $181.00  
  Purchase #3 $206.39   4.135%   $214.9242   $214.92   $214.90   $214.90  
  Purchase #4 $125.48   9.297%   $137.1459   $137.15   $137.15   $137.10  
  Purchase #5 $118.37   10.399%   $130.6793   $130.68   $130.70   $130.70  
  Purchase #6 $177.64   3.824%   $184.433   $184.43   $184.45   $184.40  
  Purchase #7 $38.94   6.183%   $41.3477   $41.35   $41.35   $41.30  
  7 purchase totals = $895.89       $957.7634   $957.76   $957.75   $957.70