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	$42.77	12.774%	$48.2334	$48.23	$48.25	$48.20
Purchase #2	$31.67	9.183%	$34.5783	$34.58	$34.60	$34.60
Purchase #3	$205.70	13.513%	$233.4962	$233.50	$233.50	$233.50
Purchase #4	$95.29	10.713%	$105.4984	$105.50	$105.50	$105.50
Purchase #5	$88.59	12.571%	$99.7266	$99.73	$99.75	$99.70
Purchase #6	$128.64	11.269%	$143.1364	$143.14	$143.15	$143.10
Purchase #7	$106.91	8.568%	$116.07	$116.07	$116.05	$116.10
7 purchase totals =	$699.57		$780.7393	$780.75	$780.80	$780.70