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 $127.59   10.591%   $141.1031   $141.10   $141.10   $141.10  
  Purchase #2 $240.90   5.793%   $254.8553   $254.86   $254.85   $254.90  
  Purchase #3 $248.86   5.657%   $262.938   $262.94   $262.95   $262.90  
  Purchase #4 $240.55   7.780%   $259.2648   $259.26   $259.25   $259.30  
  Purchase #5 $119.97   4.237%   $125.0531   $125.05   $125.05   $125.10  
  Purchase #6 $205.43   5.526%   $216.7821   $216.78   $216.80   $216.80  
  Purchase #7 $103.55   10.371%   $114.2892   $114.29   $114.30   $114.30  
  7 purchase totals = $1,286.85       $1,374.2856   $1,374.28   $1,374.30   $1,374.40