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 $197.69   11.414%   $220.2543   $220.25   $220.25   $220.30  
  Purchase #2 $33.39   6.719%   $35.6335   $35.63   $35.65   $35.60  
  Purchase #3 $90.83   8.704%   $98.7358   $98.74   $98.75   $98.70  
  Purchase #4 $178.28   9.471%   $195.1649   $195.16   $195.15   $195.20  
  Purchase #5 $229.34   5.749%   $242.5248   $242.52   $242.50   $242.50  
  Purchase #6 $44.38   12.725%   $50.0274   $50.03   $50.05   $50.00  
  Purchase #7 $108.47   13.551%   $123.1688   $123.17   $123.15   $123.20  
  7 purchase totals = $882.38       $965.5095   $965.50   $965.50   $965.50