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 $186.50   11.398%   $207.7573   $207.76   $207.75   $207.80  
  Purchase #2 $88.89   10.583%   $98.2972   $98.30   $98.30   $98.30  
  Purchase #3 $144.77   10.712%   $160.2778   $160.28   $160.30   $160.30  
  Purchase #4 $152.27   10.443%   $168.1716   $168.17   $168.15   $168.20  
  Purchase #5 $62.83   7.212%   $67.3613   $67.36   $67.35   $67.40  
  Purchase #6 $213.91   13.474%   $242.7322   $242.73   $242.75   $242.70  
  Purchase #7 $91.63   7.690%   $98.6763   $98.68   $98.70   $98.70  
  7 purchase totals = $940.80       $1,043.2737   $1,043.28   $1,043.30   $1,043.40