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 $111.87   6.358%   $118.9827   $118.98   $119.00   $119.00  
  Purchase #2 $69.66   5.286%   $73.3422   $73.34   $73.35   $73.30  
  Purchase #3 $51.30   11.873%   $57.3908   $57.39   $57.40   $57.40  
  Purchase #4 $192.29   10.246%   $211.992   $211.99   $212.00   $212.00  
  Purchase #5 $57.86   8.538%   $62.8001   $62.80   $62.80   $62.80  
  Purchase #6 $190.81   11.438%   $212.6348   $212.63   $212.65   $212.60  
  Purchase #7 $220.91   13.264%   $250.2115   $250.21   $250.20   $250.20  
  7 purchase totals = $894.70       $987.3541   $987.34   $987.40   $987.30