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	$240.62	4.514%	$251.4816	$251.48	$251.50	$251.50
Purchase #2	$125.54	6.525%	$133.7315	$133.73	$133.75	$133.70
Purchase #3	$128.60	10.824%	$142.5197	$142.52	$142.50	$142.50
Purchase #4	$80.63	12.463%	$90.6789	$90.68	$90.70	$90.70
Purchase #5	$46.82	4.208%	$48.7902	$48.79	$48.80	$48.80
Purchase #6	$175.42	5.113%	$184.3892	$184.39	$184.40	$184.40
Purchase #7	$116.65	9.418%	$127.6361	$127.64	$127.65	$127.60
7 purchase totals =	$914.28		$979.2272	$979.23	$979.30	$979.20