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 $87.37   4.856%   $91.6127   $91.61   $91.60   $91.60  
  Purchase #2 $51.38   9.303%   $56.1599   $56.16   $56.15   $56.20  
  Purchase #3 $193.62   7.645%   $208.4222   $208.42   $208.40   $208.40  
  Purchase #4 $73.99   5.706%   $78.2119   $78.21   $78.20   $78.20  
  Purchase #5 $206.59   9.323%   $225.8504   $225.85   $225.85   $225.90  
  Purchase #6 $110.99   4.813%   $116.3319   $116.33   $116.35   $116.30  
  Purchase #7 $167.27   11.544%   $186.5796   $186.58   $186.60   $186.60  
  7 purchase totals = $891.21       $963.1686   $963.16   $963.15   $963.20