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 $208.87   11.387%   $232.654   $232.65   $232.65   $232.70  
  Purchase #2 $96.87   5.629%   $102.3228   $102.32   $102.30   $102.30  
  Purchase #3 $40.42   5.737%   $42.7389   $42.74   $42.75   $42.70  
  Purchase #4 $113.89   4.805%   $119.3624   $119.36   $119.35   $119.40  
  Purchase #5 $61.83   10.184%   $68.1268   $68.13   $68.15   $68.10  
  Purchase #6 $140.82   6.808%   $150.407   $150.41   $150.40   $150.40  
  Purchase #7 $96.35   7.225%   $103.3113   $103.31   $103.30   $103.30  
  7 purchase totals = $759.05       $818.9232   $818.92   $818.90   $818.90