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 $185.59   12.132%   $208.1058   $208.11   $208.10   $208.10  
  Purchase #2 $69.74   7.198%   $74.7599   $74.76   $74.75   $74.80  
  Purchase #3 $23.81   8.144%   $25.7491   $25.75   $25.75   $25.70  
  Purchase #4 $199.53   7.416%   $214.3271   $214.33   $214.35   $214.30  
  Purchase #5 $78.42   4.533%   $81.9748   $81.97   $81.95   $82.00  
  Purchase #6 $213.43   5.632%   $225.4504   $225.45   $225.45   $225.50  
  Purchase #7 $62.63   3.537%   $64.8452   $64.85   $64.85   $64.80  
  7 purchase totals = $833.15       $895.2123   $895.22   $895.20   $895.20