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 $126.72   6.363%   $134.7832   $134.78   $134.80   $134.80  
  Purchase #2 $173.46   13.104%   $196.1902   $196.19   $196.20   $196.20  
  Purchase #3 $114.36   7.453%   $122.8833   $122.88   $122.90   $122.90  
  Purchase #4 $92.44   12.562%   $104.0523   $104.05   $104.05   $104.10  
  Purchase #5 $67.92   4.752%   $71.1476   $71.15   $71.15   $71.10  
  Purchase #6 $12.83   7.216%   $13.7558   $13.76   $13.75   $13.80  
  Purchase #7 $209.81   8.821%   $228.3173   $228.32   $228.30   $228.30  
  7 purchase totals = $797.54       $871.1297   $871.13   $871.15   $871.20