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 $61.64   7.462%   $66.2396   $66.24   $66.25   $66.20  
  Purchase #2 $227.87   6.315%   $242.26   $242.26   $242.25   $242.30  
  Purchase #3 $45.77   4.324%   $47.7491   $47.75   $47.75   $47.70  
  Purchase #4 $168.93   8.171%   $182.7333   $182.73   $182.75   $182.70  
  Purchase #5 $192.64   9.159%   $210.2839   $210.28   $210.30   $210.30  
  Purchase #6 $136.90   11.778%   $153.0241   $153.02   $153.00   $153.00  
  Purchase #7 $92.39   11.559%   $103.0694   $103.07   $103.05   $103.10  
  7 purchase totals = $926.14       $1,005.3594   $1,005.35   $1,005.35   $1,005.30