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	$50.37	10.756%	$55.7878	$55.79	$55.80	$55.80
Purchase #2	$43.36	5.150%	$45.593	$45.59	$45.60	$45.60
Purchase #3	$62.49	13.282%	$70.7899	$70.79	$70.80	$70.80
Purchase #4	$95.72	7.308%	$102.7152	$102.72	$102.70	$102.70
Purchase #5	$84.51	7.483%	$90.8339	$90.83	$90.85	$90.80
Purchase #6	$140.54	4.111%	$146.3176	$146.32	$146.30	$146.30
Purchase #7	$10.89	13.526%	$12.363	$12.36	$12.35	$12.40
7 purchase totals =	$487.88		$524.4004	$524.40	$524.40	$524.40