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 $57.81   9.766%   $63.4557   $63.46   $63.45   $63.50  
  Purchase #2 $244.67   8.821%   $266.2523   $266.25   $266.25   $266.30  
  Purchase #3 $153.43   10.620%   $169.7243   $169.72   $169.70   $169.70  
  Purchase #4 $70.90   13.510%   $80.4786   $80.48   $80.50   $80.50  
  Purchase #5 $214.75   11.587%   $239.6331   $239.63   $239.65   $239.60  
  Purchase #6 $30.97   3.377%   $32.0159   $32.02   $32.00   $32.00  
  Purchase #7 $180.27   10.554%   $199.2957   $199.30   $199.30   $199.30  
  7 purchase totals = $952.80       $1,050.8556   $1,050.86   $1,050.85   $1,050.90