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 $250.47   4.292%   $261.2202   $261.22   $261.20   $261.20  
  Purchase #2 $132.77   6.829%   $141.8369   $141.84   $141.85   $141.80  
  Purchase #3 $111.49   8.817%   $121.3201   $121.32   $121.30   $121.30  
  Purchase #4 $178.88   7.427%   $192.1654   $192.17   $192.15   $192.20  
  Purchase #5 $53.38   11.350%   $59.4386   $59.44   $59.45   $59.40  
  Purchase #6 $236.40   7.545%   $254.2364   $254.24   $254.25   $254.20  
  Purchase #7 $9.75   12.165%   $10.9361   $10.94   $10.95   $10.90  
  7 purchase totals = $973.14       $1,041.1537   $1,041.17   $1,041.15   $1,041.00