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 $92.41   11.716%   $103.2368   $103.24   $103.25   $103.20  
  Purchase #2 $234.76   7.227%   $251.7261   $251.73   $251.75   $251.70  
  Purchase #3 $107.95   7.712%   $116.2751   $116.28   $116.30   $116.30  
  Purchase #4 $175.72   5.609%   $185.5761   $185.58   $185.60   $185.60  
  Purchase #5 $131.83   3.544%   $136.5021   $136.50   $136.50   $136.50  
  Purchase #6 $236.74   6.644%   $252.469   $252.47   $252.45   $252.50  
  Purchase #7 $171.34   4.215%   $178.562   $178.56   $178.55   $178.60  
  7 purchase totals = $1,150.75       $1,224.3472   $1,224.36   $1,224.40   $1,224.40