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	$141.99	3.374%	$146.7807	$146.78	$146.80	$146.80
Purchase #2	$127.52	12.622%	$143.6156	$143.62	$143.60	$143.60
Purchase #3	$95.70	10.567%	$105.8126	$105.81	$105.80	$105.80
Purchase #4	$175.82	11.859%	$196.6705	$196.67	$196.65	$196.70
Purchase #5	$151.28	13.778%	$172.1234	$172.12	$172.10	$172.10
Purchase #6	$212.31	13.421%	$240.8041	$240.80	$240.80	$240.80
Purchase #7	$118.26	4.860%	$124.0074	$124.01	$124.00	$124.00
7 purchase totals =	$1,022.88		$1,129.8143	$1,129.81	$1,129.75	$1,129.80