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 $44.72   4.182%   $46.5902   $46.59   $46.60   $46.60  
  Purchase #2 $129.44   7.429%   $139.0561   $139.06   $139.05   $139.10  
  Purchase #3 $167.48   5.330%   $176.4067   $176.41   $176.40   $176.40  
  Purchase #4 $148.63   6.440%   $158.2018   $158.20   $158.20   $158.20  
  Purchase #5 $152.25   3.468%   $157.53   $157.53   $157.55   $157.50  
  Purchase #6 $65.94   4.559%   $68.9462   $68.95   $68.95   $68.90  
  Purchase #7 $219.81   11.325%   $244.7035   $244.70   $244.70   $244.70  
  7 purchase totals = $928.27       $991.4345   $991.44   $991.45   $991.40