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	$100.59	6.450%	$107.0781	$107.08	$107.10	$107.10
Purchase #2	$98.32	13.833%	$111.9206	$111.92	$111.90	$111.90
Purchase #3	$30.74	12.440%	$34.5641	$34.56	$34.55	$34.60
Purchase #4	$178.47	6.697%	$190.4221	$190.42	$190.40	$190.40
Purchase #5	$159.32	3.803%	$165.3789	$165.38	$165.40	$165.40
Purchase #6	$29.71	8.111%	$32.1198	$32.12	$32.10	$32.10
Purchase #7	$246.64	12.623%	$277.7734	$277.77	$277.75	$277.80
7 purchase totals =	$843.79		$919.2570	$919.25	$919.20	$919.30