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	$44.92	9.598%	$49.2314	$49.23	$49.25	$49.20
Purchase #2	$178.70	11.591%	$199.4131	$199.41	$199.40	$199.40
Purchase #3	$65.39	12.805%	$73.7632	$73.76	$73.75	$73.80
Purchase #4	$140.54	9.364%	$153.7002	$153.70	$153.70	$153.70
Purchase #5	$108.52	13.758%	$123.4502	$123.45	$123.45	$123.50
Purchase #6	$105.93	13.563%	$120.2973	$120.30	$120.30	$120.30
Purchase #7	$100.72	13.669%	$114.4874	$114.49	$114.50	$114.50
7 purchase totals =	$744.72		$834.3428	$834.34	$834.35	$834.40