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 $248.58   5.399%   $262.0008   $262.00   $262.00   $262.00  
  Purchase #2 $66.55   7.697%   $71.6724   $71.67   $71.65   $71.70  
  Purchase #3 $98.55   8.140%   $106.572   $106.57   $106.55   $106.60  
  Purchase #4 $242.54   4.376%   $253.1536   $253.15   $253.15   $253.20  
  Purchase #5 $53.91   3.867%   $55.9947   $55.99   $56.00   $56.00  
  Purchase #6 $137.29   5.729%   $145.1553   $145.16   $145.15   $145.20  
  Purchase #7 $238.46   12.819%   $269.0282   $269.03   $269.05   $269.00  
  7 purchase totals = $1,085.88       $1,163.5770   $1,163.57   $1,163.55   $1,163.70