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	$18.27	13.429%	$20.7235	$20.72	$20.70	$20.70
Purchase #2	$183.32	9.368%	$200.4934	$200.49	$200.50	$200.50
Purchase #3	$139.48	9.523%	$152.7627	$152.76	$152.75	$152.80
Purchase #4	$211.72	9.784%	$232.4347	$232.43	$232.45	$232.40
Purchase #5	$236.47	4.624%	$247.4044	$247.40	$247.40	$247.40
Purchase #6	$204.85	5.137%	$215.3731	$215.37	$215.35	$215.40
Purchase #7	$157.38	9.575%	$172.4491	$172.45	$172.45	$172.40
7 purchase totals =	$1,151.49		$1,241.6409	$1,241.62	$1,241.60	$1,241.60