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 $185.26   7.662%   $199.4546   $199.45   $199.45   $199.50  
  Purchase #2 $15.97   9.150%   $17.4313   $17.43   $17.45   $17.40  
  Purchase #3 $52.94   3.545%   $54.8167   $54.82   $54.80   $54.80  
  Purchase #4 $222.56   8.493%   $241.462   $241.46   $241.45   $241.50  
  Purchase #5 $241.91   10.324%   $266.8848   $266.88   $266.90   $266.90  
  Purchase #6 $119.41   6.647%   $127.3472   $127.35   $127.35   $127.30  
  Purchase #7 $173.30   12.532%   $195.018   $195.02   $195.00   $195.00  
  7 purchase totals = $1,011.35       $1,102.4146   $1,102.41   $1,102.40   $1,102.40