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 $87.44   12.265%   $98.1645   $98.16   $98.15   $98.20  
  Purchase #2 $50.97   13.586%   $57.8948   $57.89   $57.90   $57.90  
  Purchase #3 $118.37   12.794%   $133.5143   $133.51   $133.50   $133.50  
  Purchase #4 $231.68   7.152%   $248.2498   $248.25   $248.25   $248.20  
  Purchase #5 $234.59   7.106%   $251.26   $251.26   $251.25   $251.30  
  Purchase #6 $159.47   3.294%   $164.7229   $164.72   $164.70   $164.70  
  Purchase #7 $52.69   9.392%   $57.6386   $57.64   $57.65   $57.60  
  7 purchase totals = $935.21       $1,011.4449   $1,011.43   $1,011.40   $1,011.40