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	$165.74	3.488%	$171.521	$171.52	$171.50	$171.50
Purchase #2	$94.86	10.362%	$104.6894	$104.69	$104.70	$104.70
Purchase #3	$105.87	5.611%	$111.8104	$111.81	$111.80	$111.80
Purchase #4	$124.72	4.611%	$130.4708	$130.47	$130.45	$130.50
Purchase #5	$211.62	5.291%	$222.8168	$222.82	$222.80	$222.80
Purchase #6	$148.25	10.377%	$163.6339	$163.63	$163.65	$163.60
Purchase #7	$97.84	4.553%	$102.2947	$102.29	$102.30	$102.30
7 purchase totals =	$948.90		$1,007.2370	$1,007.23	$1,007.20	$1,007.20