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 $242.91   13.682%   $276.1449   $276.14   $276.15   $276.10  
  Purchase #2 $161.47   9.156%   $176.2542   $176.25   $176.25   $176.30  
  Purchase #3 $170.26   13.283%   $192.8756   $192.88   $192.90   $192.90  
  Purchase #4 $100.94   8.162%   $109.1787   $109.18   $109.20   $109.20  
  Purchase #5 $125.80   6.197%   $133.5958   $133.60   $133.60   $133.60  
  Purchase #6 $81.93   5.856%   $86.7278   $86.73   $86.75   $86.70  
  Purchase #7 $47.85   10.333%   $52.7943   $52.79   $52.80   $52.80  
  7 purchase totals = $931.16       $1,027.5713   $1,027.57   $1,027.65   $1,027.60