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	$128.84	13.621%	$146.3893	$146.39	$146.40	$146.40
Purchase #2	$179.91	4.794%	$188.5349	$188.53	$188.55	$188.50
Purchase #3	$141.72	12.534%	$159.4832	$159.48	$159.50	$159.50
Purchase #4	$95.44	3.471%	$98.7527	$98.75	$98.75	$98.80
Purchase #5	$80.74	9.679%	$88.5548	$88.55	$88.55	$88.60
Purchase #6	$143.28	5.741%	$151.5057	$151.51	$151.50	$151.50
Purchase #7	$10.27	12.191%	$11.522	$11.52	$11.50	$11.50
7 purchase totals =	$780.20		$844.7426	$844.73	$844.75	$844.80