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 $40.46   8.461%   $43.8833   $43.88   $43.90   $43.90  
  Purchase #2 $232.96   12.156%   $261.2786   $261.28   $261.30   $261.30  
  Purchase #3 $24.46   6.224%   $25.9824   $25.98   $26.00   $26.00  
  Purchase #4 $94.64   9.589%   $103.715   $103.72   $103.70   $103.70  
  Purchase #5 $192.29   11.593%   $214.5822   $214.58   $214.60   $214.60  
  Purchase #6 $18.82   6.187%   $19.9844   $19.98   $20.00   $20.00  
  Purchase #7 $224.53   10.672%   $248.4918   $248.49   $248.50   $248.50  
  7 purchase totals = $828.16       $917.9177   $917.91   $918.00   $918.00