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 $38.41   12.441%   $43.1886   $43.19   $43.20   $43.20  
  Purchase #2 $140.28   8.194%   $151.7745   $151.77   $151.75   $151.80  
  Purchase #3 $206.25   3.663%   $213.8049   $213.80   $213.80   $213.80  
  Purchase #4 $99.67   11.214%   $110.847   $110.85   $110.85   $110.80  
  Purchase #5 $242.97   10.762%   $269.1184   $269.12   $269.10   $269.10  
  Purchase #6 $199.44   7.317%   $214.033   $214.03   $214.05   $214.00  
  Purchase #7 $190.99   8.174%   $206.6015   $206.60   $206.60   $206.60  
  7 purchase totals = $1,118.01       $1,209.3679   $1,209.36   $1,209.35   $1,209.30