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 $233.69   3.138%   $241.0232   $241.02   $241.00   $241.00  
  Purchase #2 $133.69   11.518%   $149.0884   $149.09   $149.10   $149.10  
  Purchase #3 $5.79   7.559%   $6.2277   $6.23   $6.25   $6.20  
  Purchase #4 $84.92   12.680%   $95.6879   $95.69   $95.70   $95.70  
  Purchase #5 $68.86   8.491%   $74.7069   $74.71   $74.70   $74.70  
  Purchase #6 $69.81   7.429%   $74.9962   $75.00   $75.00   $75.00  
  Purchase #7 $16.92   5.354%   $17.8259   $17.83   $17.85   $17.80  
  7 purchase totals = $613.68       $659.5562   $659.57   $659.60   $659.50