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 $249.31   5.396%   $262.7628   $262.76   $262.75   $262.80  
  Purchase #2 $242.66   10.543%   $268.2436   $268.24   $268.25   $268.20  
  Purchase #3 $22.54   6.130%   $23.9217   $23.92   $23.90   $23.90  
  Purchase #4 $232.98   13.122%   $263.5516   $263.55   $263.55   $263.60  
  Purchase #5 $206.83   5.163%   $217.5086   $217.51   $217.50   $217.50  
  Purchase #6 $147.54   3.132%   $152.161   $152.16   $152.15   $152.20  
  Purchase #7 $158.99   4.257%   $165.7582   $165.76   $165.75   $165.80  
  7 purchase totals = $1,260.85       $1,353.9075   $1,353.90   $1,353.85   $1,354.00