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 $180.30   13.758%   $205.1057   $205.11   $205.10   $205.10  
  Purchase #2 $189.53   13.249%   $214.6408   $214.64   $214.65   $214.60  
  Purchase #3 $72.68   3.429%   $75.1722   $75.17   $75.15   $75.20  
  Purchase #4 $116.28   11.168%   $129.2662   $129.27   $129.25   $129.30  
  Purchase #5 $52.48   10.369%   $57.9217   $57.92   $57.90   $57.90  
  Purchase #6 $202.30   11.118%   $224.7917   $224.79   $224.80   $224.80  
  Purchase #7 $122.90   13.130%   $139.0368   $139.04   $139.05   $139.00  
  7 purchase totals = $936.47       $1,045.9351   $1,045.94   $1,045.90   $1,045.90