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 $162.51   8.606%   $176.4956   $176.50   $176.50   $176.50  
  Purchase #2 $250.36   10.541%   $276.7504   $276.75   $276.75   $276.80  
  Purchase #3 $173.76   3.861%   $180.4689   $180.47   $180.45   $180.50  
  Purchase #4 $82.69   10.671%   $91.5138   $91.51   $91.50   $91.50  
  Purchase #5 $22.92   5.182%   $24.1077   $24.11   $24.10   $24.10  
  Purchase #6 $67.97   9.775%   $74.6141   $74.61   $74.60   $74.60  
  Purchase #7 $73.34   11.771%   $81.9729   $81.97   $81.95   $82.00  
  7 purchase totals = $833.55       $905.9234   $905.92   $905.85   $906.00