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 $114.95   9.239%   $125.5702   $125.57   $125.55   $125.60  
  Purchase #2 $22.54   7.707%   $24.2772   $24.28   $24.30   $24.30  
  Purchase #3 $30.99   9.384%   $33.8981   $33.90   $33.90   $33.90  
  Purchase #4 $231.32   6.205%   $245.6734   $245.67   $245.65   $245.70  
  Purchase #5 $189.89   9.561%   $208.0454   $208.05   $208.05   $208.00  
  Purchase #6 $12.72   7.194%   $13.6351   $13.64   $13.65   $13.60  
  Purchase #7 $66.65   9.410%   $72.9218   $72.92   $72.90   $72.90  
  7 purchase totals = $669.06       $724.0212   $724.03   $724.00   $724.00