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 $55.44   13.518%   $62.9344   $62.93   $62.95   $62.90  
  Purchase #2 $27.98   9.212%   $30.5575   $30.56   $30.55   $30.60  
  Purchase #3 $90.85   5.254%   $95.6233   $95.62   $95.60   $95.60  
  Purchase #4 $38.81   10.312%   $42.8121   $42.81   $42.80   $42.80  
  Purchase #5 $246.99   4.393%   $257.8403   $257.84   $257.85   $257.80  
  Purchase #6 $127.48   11.197%   $141.7539   $141.75   $141.75   $141.80  
  Purchase #7 $125.86   5.293%   $132.5218   $132.52   $132.50   $132.50  
  7 purchase totals = $713.41       $764.0433   $764.03   $764.00   $764.00