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	$243.74	5.582%	$257.3456	$257.35	$257.35	$257.30
Purchase #2	$33.76	12.356%	$37.9314	$37.93	$37.95	$37.90
Purchase #3	$244.45	4.267%	$254.8807	$254.88	$254.90	$254.90
Purchase #4	$103.76	3.838%	$107.7423	$107.74	$107.75	$107.70
Purchase #5	$88.70	4.404%	$92.6063	$92.61	$92.60	$92.60
Purchase #6	$110.64	11.520%	$123.3857	$123.39	$123.40	$123.40
Purchase #7	$126.60	5.537%	$133.6098	$133.61	$133.60	$133.60
7 purchase totals =	$951.65		$1,007.5018	$1,007.51	$1,007.55	$1,007.40