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	$65.28	7.283%	$70.0343	$70.03	$70.05	$70.00
Purchase #2	$195.27	8.351%	$211.577	$211.58	$211.60	$211.60
Purchase #3	$124.93	10.146%	$137.6054	$137.61	$137.60	$137.60
Purchase #4	$149.70	6.430%	$159.3257	$159.33	$159.35	$159.30
Purchase #5	$113.75	12.108%	$127.5229	$127.52	$127.50	$127.50
Purchase #6	$64.64	12.657%	$72.8215	$72.82	$72.80	$72.80
Purchase #7	$227.35	5.234%	$239.2495	$239.25	$239.25	$239.20
7 purchase totals =	$940.92		$1,018.1363	$1,018.14	$1,018.15	$1,018.00