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 $59.98   13.342%   $67.9825   $67.98   $68.00   $68.00  
  Purchase #2 $219.90   5.679%   $232.3881   $232.39   $232.40   $232.40  
  Purchase #3 $59.26   6.634%   $63.1913   $63.19   $63.20   $63.20  
  Purchase #4 $185.71   10.327%   $204.8883   $204.89   $204.90   $204.90  
  Purchase #5 $192.95   11.336%   $214.8228   $214.82   $214.80   $214.80  
  Purchase #6 $119.70   8.423%   $129.7823   $129.78   $129.80   $129.80  
  Purchase #7 $69.70   13.422%   $79.0551   $79.06   $79.05   $79.10  
  7 purchase totals = $907.20       $992.1104   $992.11   $992.15   $992.20