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 $192.26   8.311%   $208.2387   $208.24   $208.25   $208.20  
  Purchase #2 $111.94   4.792%   $117.3042   $117.30   $117.30   $117.30  
  Purchase #3 $121.57   10.181%   $133.947   $133.95   $133.95   $133.90  
  Purchase #4 $210.74   13.328%   $238.8274   $238.83   $238.85   $238.80  
  Purchase #5 $219.94   4.621%   $230.1034   $230.10   $230.10   $230.10  
  Purchase #6 $135.32   4.131%   $140.9101   $140.91   $140.90   $140.90  
  Purchase #7 $249.49   5.777%   $263.903   $263.90   $263.90   $263.90  
  7 purchase totals = $1,241.26       $1,333.2338   $1,333.23   $1,333.25   $1,333.10