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 $221.53   11.129%   $246.1841   $246.18   $246.20   $246.20  
  Purchase #2 $96.56   6.240%   $102.5853   $102.59   $102.60   $102.60  
  Purchase #3 $127.95   10.804%   $141.7737   $141.77   $141.75   $141.80  
  Purchase #4 $197.32   5.777%   $208.7192   $208.72   $208.70   $208.70  
  Purchase #5 $81.63   10.511%   $90.2101   $90.21   $90.20   $90.20  
  Purchase #6 $138.79   5.661%   $146.6469   $146.65   $146.65   $146.60  
  Purchase #7 $78.74   9.453%   $86.1833   $86.18   $86.20   $86.20  
  7 purchase totals = $942.52       $1,022.3026   $1,022.30   $1,022.30   $1,022.30