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	$135.44	8.286%	$146.6626	$146.66	$146.65	$146.70
Purchase #2	$16.91	13.797%	$19.2431	$19.24	$19.25	$19.20
Purchase #3	$173.52	5.111%	$182.3886	$182.39	$182.40	$182.40
Purchase #4	$86.54	13.553%	$98.2688	$98.27	$98.25	$98.30
Purchase #5	$101.40	10.373%	$111.9182	$111.92	$111.90	$111.90
Purchase #6	$184.50	6.654%	$196.7766	$196.78	$196.80	$196.80
Purchase #7	$158.53	11.331%	$176.493	$176.49	$176.50	$176.50
7 purchase totals =	$856.84		$931.7509	$931.75	$931.75	$931.80