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 $247.38   8.785%   $269.1123   $269.11   $269.10   $269.10  
  Purchase #2 $168.90   4.348%   $176.2438   $176.24   $176.25   $176.20  
  Purchase #3 $187.95   13.213%   $212.7838   $212.78   $212.80   $212.80  
  Purchase #4 $222.63   3.275%   $229.9211   $229.92   $229.90   $229.90  
  Purchase #5 $100.62   12.838%   $113.5376   $113.54   $113.55   $113.50  
  Purchase #6 $58.61   4.605%   $61.309   $61.31   $61.30   $61.30  
  Purchase #7 $197.39   4.406%   $206.087   $206.09   $206.10   $206.10  
  7 purchase totals = $1,183.48       $1,268.9946   $1,268.99   $1,269.00   $1,268.90