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 $164.83   12.364%   $185.2096   $185.21   $185.20   $185.20  
  Purchase #2 $68.62   12.397%   $77.1268   $77.13   $77.15   $77.10  
  Purchase #3 $117.92   3.376%   $121.901   $121.90   $121.90   $121.90  
  Purchase #4 $217.66   4.549%   $227.5614   $227.56   $227.55   $227.60  
  Purchase #5 $56.80   6.538%   $60.5136   $60.51   $60.50   $60.50  
  Purchase #6 $38.54   5.589%   $40.694   $40.69   $40.70   $40.70  
  Purchase #7 $169.30   8.672%   $183.9817   $183.98   $184.00   $184.00  
  7 purchase totals = $833.67       $896.9881   $896.98   $897.00   $897.00