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 $62.91   10.684%   $69.6313   $69.63   $69.65   $69.60  
  Purchase #2 $215.26   5.633%   $227.3856   $227.39   $227.40   $227.40  
  Purchase #3 $232.34   5.332%   $244.7284   $244.73   $244.75   $244.70  
  Purchase #4 $45.25   12.102%   $50.7262   $50.73   $50.75   $50.70  
  Purchase #5 $166.49   7.696%   $179.3031   $179.30   $179.30   $179.30  
  Purchase #6 $138.95   9.281%   $151.8459   $151.85   $151.85   $151.80  
  Purchase #7 $74.49   5.743%   $78.768   $78.77   $78.75   $78.80  
  7 purchase totals = $935.69       $1,002.3885   $1,002.40   $1,002.45   $1,002.30