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	$100.94	10.660%	$111.7002	$111.70	$111.70	$111.70
Purchase #2	$165.35	4.339%	$172.5245	$172.52	$172.50	$172.50
Purchase #3	$25.78	11.713%	$28.7996	$28.80	$28.80	$28.80
Purchase #4	$143.56	3.441%	$148.4999	$148.50	$148.50	$148.50
Purchase #5	$125.28	11.405%	$139.5682	$139.57	$139.55	$139.60
Purchase #6	$202.88	3.301%	$209.5771	$209.58	$209.60	$209.60
Purchase #7	$62.44	10.613%	$69.0668	$69.07	$69.05	$69.10
7 purchase totals =	$826.23		$879.7363	$879.74	$879.70	$879.80