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 $248.42   10.132%   $273.5899   $273.59   $273.60   $273.60  
  Purchase #2 $130.36   4.250%   $135.9003   $135.90   $135.90   $135.90  
  Purchase #3 $86.92   5.359%   $91.578   $91.58   $91.60   $91.60  
  Purchase #4 $234.41   3.624%   $242.905   $242.91   $242.90   $242.90  
  Purchase #5 $142.96   11.163%   $158.9186   $158.92   $158.90   $158.90  
  Purchase #6 $220.62   5.443%   $232.6283   $232.63   $232.65   $232.60  
  Purchase #7 $58.96   12.522%   $66.343   $66.34   $66.35   $66.30  
  7 purchase totals = $1,122.65       $1,201.8631   $1,201.87   $1,201.90   $1,201.80