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 $79.61   8.780%   $86.5998   $86.60   $86.60   $86.60  
  Purchase #2 $185.78   4.527%   $194.1903   $194.19   $194.20   $194.20  
  Purchase #3 $169.45   4.233%   $176.6228   $176.62   $176.60   $176.60  
  Purchase #4 $67.97   8.871%   $73.9996   $74.00   $74.00   $74.00  
  Purchase #5 $60.62   5.864%   $64.1748   $64.17   $64.15   $64.20  
  Purchase #6 $192.97   7.782%   $207.9869   $207.99   $208.00   $208.00  
  Purchase #7 $24.93   13.512%   $28.2985   $28.30   $28.30   $28.30  
  7 purchase totals = $781.33       $831.8727   $831.87   $831.85   $831.90