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 $66.69   10.812%   $73.9005   $73.90   $73.90   $73.90  
  Purchase #2 $114.49   4.583%   $119.7371   $119.74   $119.75   $119.70  
  Purchase #3 $249.61   3.774%   $259.0303   $259.03   $259.05   $259.00  
  Purchase #4 $191.46   4.232%   $199.5626   $199.56   $199.55   $199.60  
  Purchase #5 $60.79   7.403%   $65.2903   $65.29   $65.30   $65.30  
  Purchase #6 $172.84   7.750%   $186.2351   $186.24   $186.25   $186.20  
  Purchase #7 $114.71   8.450%   $124.403   $124.40   $124.40   $124.40  
  7 purchase totals = $970.59       $1,028.1589   $1,028.16   $1,028.20   $1,028.10