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	$242.35	3.518%	$250.8759	$250.88	$250.90	$250.90
Purchase #2	$199.89	3.286%	$206.4584	$206.46	$206.45	$206.50
Purchase #3	$190.49	7.748%	$205.2492	$205.25	$205.25	$205.20
Purchase #4	$51.27	6.326%	$54.5133	$54.51	$54.50	$54.50
Purchase #5	$239.74	13.696%	$272.5748	$272.57	$272.55	$272.60
Purchase #6	$91.62	11.820%	$102.4495	$102.45	$102.45	$102.40
Purchase #7	$147.46	9.487%	$161.4495	$161.45	$161.45	$161.40
7 purchase totals =	$1,162.82		$1,253.5706	$1,253.57	$1,253.55	$1,253.50