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 $9.25   3.707%   $9.5929   $9.59   $9.60   $9.60  
  Purchase #2 $247.73   6.283%   $263.2949   $263.29   $263.30   $263.30  
  Purchase #3 $231.31   13.495%   $262.5253   $262.53   $262.55   $262.50  
  Purchase #4 $27.86   8.842%   $30.3234   $30.32   $30.30   $30.30  
  Purchase #5 $110.45   3.237%   $114.0253   $114.03   $114.05   $114.00  
  Purchase #6 $249.56   5.421%   $263.0886   $263.09   $263.10   $263.10  
  Purchase #7 $38.90   12.319%   $43.6921   $43.69   $43.70   $43.70  
  7 purchase totals = $915.06       $986.5425   $986.54   $986.60   $986.50