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	$123.33	12.319%	$138.523	$138.52	$138.50	$138.50
Purchase #2	$105.90	5.539%	$111.7658	$111.77	$111.75	$111.80
Purchase #3	$245.56	3.682%	$254.6015	$254.60	$254.60	$254.60
Purchase #4	$97.83	6.235%	$103.9297	$103.93	$103.95	$103.90
Purchase #5	$118.59	4.711%	$124.1768	$124.18	$124.20	$124.20
Purchase #6	$140.90	12.460%	$158.4561	$158.46	$158.45	$158.50
Purchase #7	$240.60	10.423%	$265.6777	$265.68	$265.70	$265.70
7 purchase totals =	$1,072.71		$1,157.1306	$1,157.14	$1,157.15	$1,157.20