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 $39.69   4.852%   $41.6158   $41.62   $41.60   $41.60  
  Purchase #2 $229.75   11.329%   $255.7784   $255.78   $255.80   $255.80  
  Purchase #3 $144.80   13.476%   $164.3132   $164.31   $164.30   $164.30  
  Purchase #4 $148.37   7.794%   $159.934   $159.93   $159.95   $159.90  
  Purchase #5 $234.77   13.730%   $267.0039   $267.00   $267.00   $267.00  
  Purchase #6 $241.27   9.175%   $263.4065   $263.41   $263.40   $263.40  
  Purchase #7 $7.91   13.459%   $8.9746   $8.97   $8.95   $9.00  
  7 purchase totals = $1,046.56       $1,161.0264   $1,161.02   $1,161.00   $1,161.00