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 $157.62   8.709%   $171.3471   $171.35   $171.35   $171.30  
  Purchase #2 $78.72   9.448%   $86.1575   $86.16   $86.15   $86.20  
  Purchase #3 $27.74   5.271%   $29.2022   $29.20   $29.20   $29.20  
  Purchase #4 $101.29   10.794%   $112.2232   $112.22   $112.20   $112.20  
  Purchase #5 $231.26   13.564%   $262.6281   $262.63   $262.65   $262.60  
  Purchase #6 $152.63   11.285%   $169.8543   $169.85   $169.85   $169.90  
  Purchase #7 $76.30   4.579%   $79.7938   $79.79   $79.80   $79.80  
  7 purchase totals = $825.56       $911.2062   $911.20   $911.20   $911.20