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 $119.75   3.378%   $123.7952   $123.80   $123.80   $123.80  
  Purchase #2 $9.52   6.547%   $10.1433   $10.14   $10.15   $10.10  
  Purchase #3 $94.61   10.658%   $104.6935   $104.69   $104.70   $104.70  
  Purchase #4 $127.26   4.678%   $133.2132   $133.21   $133.20   $133.20  
  Purchase #5 $18.47   7.420%   $19.8405   $19.84   $19.85   $19.80  
  Purchase #6 $234.32   11.262%   $260.7091   $260.71   $260.70   $260.70  
  Purchase #7 $58.26   10.580%   $64.4239   $64.42   $64.40   $64.40  
  7 purchase totals = $662.19       $716.8187   $716.81   $716.80   $716.70