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	$93.61	11.527%	$104.4004	$104.40	$104.40	$104.40
Purchase #2	$143.39	11.794%	$160.3014	$160.30	$160.30	$160.30
Purchase #3	$122.78	4.475%	$128.2744	$128.27	$128.25	$128.30
Purchase #4	$71.45	4.377%	$74.5774	$74.58	$74.60	$74.60
Purchase #5	$201.35	10.606%	$222.7052	$222.71	$222.70	$222.70
Purchase #6	$19.34	6.757%	$20.6468	$20.65	$20.65	$20.60
Purchase #7	$88.52	13.718%	$100.6632	$100.66	$100.65	$100.70
7 purchase totals =	$740.44		$811.5688	$811.57	$811.55	$811.60