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 $94.82   3.594%   $98.2278   $98.23   $98.25   $98.20  
  Purchase #2 $232.38   3.720%   $241.0245   $241.02   $241.00   $241.00  
  Purchase #3 $218.54   4.286%   $227.9066   $227.91   $227.90   $227.90  
  Purchase #4 $233.92   3.162%   $241.3166   $241.32   $241.30   $241.30  
  Purchase #5 $9.49   7.204%   $10.1737   $10.17   $10.15   $10.20  
  Purchase #6 $222.34   3.117%   $229.2703   $229.27   $229.25   $229.30  
  Purchase #7 $152.88   6.550%   $162.8936   $162.89   $162.90   $162.90  
  7 purchase totals = $1,164.37       $1,210.8131   $1,210.81   $1,210.75   $1,210.80