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 $62.70   8.486%   $68.0207   $68.02   $68.00   $68.00  
  Purchase #2 $239.82   9.469%   $262.5286   $262.53   $262.55   $262.50  
  Purchase #3 $236.56   7.552%   $254.425   $254.43   $254.45   $254.40  
  Purchase #4 $214.95   11.506%   $239.6821   $239.68   $239.70   $239.70  
  Purchase #5 $143.49   6.192%   $152.3749   $152.37   $152.35   $152.40  
  Purchase #6 $199.42   6.271%   $211.9256   $211.93   $211.95   $211.90  
  Purchase #7 $130.71   8.549%   $141.8844   $141.88   $141.90   $141.90  
  7 purchase totals = $1,227.65       $1,330.8413   $1,330.84   $1,330.90   $1,330.80