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 $239.46   6.178%   $254.2538   $254.25   $254.25   $254.30  
  Purchase #2 $61.81   12.695%   $69.6568   $69.66   $69.65   $69.70  
  Purchase #3 $31.36   10.833%   $34.7572   $34.76   $34.75   $34.80  
  Purchase #4 $43.61   12.220%   $48.9391   $48.94   $48.95   $48.90  
  Purchase #5 $62.87   5.198%   $66.138   $66.14   $66.15   $66.10  
  Purchase #6 $5.57   4.308%   $5.81   $5.81   $5.80   $5.80  
  Purchase #7 $13.52   5.510%   $14.265   $14.27   $14.25   $14.30  
  7 purchase totals = $458.20       $493.8199   $493.83   $493.80   $493.90