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	$156.27	5.461%	$164.8039	$164.80	$164.80	$164.80
Purchase #2	$42.49	6.382%	$45.2017	$45.20	$45.20	$45.20
Purchase #3	$129.71	11.626%	$144.7901	$144.79	$144.80	$144.80
Purchase #4	$75.99	7.703%	$81.8435	$81.84	$81.85	$81.80
Purchase #5	$146.42	3.722%	$151.8698	$151.87	$151.85	$151.90
Purchase #6	$118.37	10.682%	$131.0143	$131.01	$131.00	$131.00
Purchase #7	$24.64	10.873%	$27.3191	$27.32	$27.30	$27.30
7 purchase totals =	$693.89		$746.8424	$746.83	$746.80	$746.80