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 $203.48   3.136%   $209.8611   $209.86   $209.85   $209.90  
  Purchase #2 $23.70   10.161%   $26.1082   $26.11   $26.10   $26.10  
  Purchase #3 $58.48   11.143%   $64.9964   $65.00   $65.00   $65.00  
  Purchase #4 $69.27   10.203%   $76.3376   $76.34   $76.35   $76.30  
  Purchase #5 $237.97   12.705%   $268.2041   $268.20   $268.20   $268.20  
  Purchase #6 $246.53   6.105%   $261.5807   $261.58   $261.60   $261.60  
  Purchase #7 $129.94   11.436%   $144.7999   $144.80   $144.80   $144.80  
  7 purchase totals = $969.37       $1,051.8880   $1,051.89   $1,051.90   $1,051.90