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	$74.31	11.126%	$82.5777	$82.58	$82.60	$82.60
Purchase #2	$31.52	9.428%	$34.4917	$34.49	$34.50	$34.50
Purchase #3	$131.69	11.782%	$147.2057	$147.21	$147.20	$147.20
Purchase #4	$28.71	10.309%	$31.6697	$31.67	$31.65	$31.70
Purchase #5	$200.83	11.113%	$223.1482	$223.15	$223.15	$223.10
Purchase #6	$104.86	6.401%	$111.5721	$111.57	$111.55	$111.60
Purchase #7	$92.84	12.751%	$104.678	$104.68	$104.70	$104.70
7 purchase totals =	$664.76		$735.3431	$735.35	$735.35	$735.40