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 $66.61   11.177%   $74.055   $74.06   $74.05   $74.10  
  Purchase #2 $248.39   9.285%   $271.453   $271.45   $271.45   $271.50  
  Purchase #3 $188.77   6.592%   $201.2137   $201.21   $201.20   $201.20  
  Purchase #4 $195.77   9.613%   $214.5894   $214.59   $214.60   $214.60  
  Purchase #5 $62.42   7.837%   $67.3119   $67.31   $67.30   $67.30  
  Purchase #6 $83.38   3.757%   $86.5126   $86.51   $86.50   $86.50  
  Purchase #7 $42.97   4.224%   $44.7851   $44.79   $44.80   $44.80  
  7 purchase totals = $888.31       $959.9207   $959.92   $959.90   $960.00