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 $91.83   3.683%   $95.2121   $95.21   $95.20   $95.20  
  Purchase #2 $77.90   4.193%   $81.1663   $81.17   $81.15   $81.20  
  Purchase #3 $54.65   12.669%   $61.5736   $61.57   $61.55   $61.60  
  Purchase #4 $108.34   8.801%   $117.875   $117.88   $117.90   $117.90  
  Purchase #5 $248.73   5.627%   $262.726   $262.73   $262.75   $262.70  
  Purchase #6 $57.32   12.763%   $64.6358   $64.64   $64.65   $64.60  
  Purchase #7 $112.58   10.338%   $124.2185   $124.22   $124.20   $124.20  
  7 purchase totals = $751.35       $807.4073   $807.42   $807.40   $807.40