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	$20.69	8.653%	$22.4803	$22.48	$22.50	$22.50
Purchase #2	$21.84	13.643%	$24.8196	$24.82	$24.80	$24.80
Purchase #3	$209.57	4.139%	$218.2441	$218.24	$218.25	$218.20
Purchase #4	$137.72	4.338%	$143.6943	$143.69	$143.70	$143.70
Purchase #5	$92.52	13.717%	$105.211	$105.21	$105.20	$105.20
Purchase #6	$163.57	10.757%	$181.1652	$181.17	$181.15	$181.20
Purchase #7	$89.78	10.135%	$98.8792	$98.88	$98.90	$98.90
7 purchase totals =	$735.69		$794.4937	$794.49	$794.50	$794.50