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	$19.91	5.535%	$21.012	$21.01	$21.00	$21.00
Purchase #2	$248.65	8.220%	$269.089	$269.09	$269.10	$269.10
Purchase #3	$148.80	4.228%	$155.0913	$155.09	$155.10	$155.10
Purchase #4	$52.68	13.180%	$59.6232	$59.62	$59.60	$59.60
Purchase #5	$244.66	9.319%	$267.4599	$267.46	$267.45	$267.50
Purchase #6	$53.25	3.570%	$55.151	$55.15	$55.15	$55.20
Purchase #7	$223.82	4.495%	$233.8807	$233.88	$233.90	$233.90
7 purchase totals =	$991.77		$1,061.3071	$1,061.30	$1,061.30	$1,061.40