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 $88.53   11.117%   $98.3719   $98.37   $98.35   $98.40  
  Purchase #2 $247.81   11.832%   $277.1309   $277.13   $277.15   $277.10  
  Purchase #3 $151.35   11.165%   $168.2482   $168.25   $168.25   $168.20  
  Purchase #4 $145.75   5.763%   $154.1496   $154.15   $154.15   $154.10  
  Purchase #5 $206.58   13.520%   $234.5096   $234.51   $234.50   $234.50  
  Purchase #6 $90.43   7.538%   $97.2466   $97.25   $97.25   $97.20  
  Purchase #7 $171.32   8.407%   $185.7229   $185.72   $185.70   $185.70  
  7 purchase totals = $1,101.77       $1,215.3797   $1,215.38   $1,215.35   $1,215.20