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	$156.54	9.548%	$171.4864	$171.49	$171.50	$171.50
Purchase #2	$49.45	3.582%	$51.2213	$51.22	$51.20	$51.20
Purchase #3	$111.97	9.105%	$122.1649	$122.16	$122.15	$122.20
Purchase #4	$181.71	5.258%	$191.2643	$191.26	$191.25	$191.30
Purchase #5	$196.59	4.581%	$205.5958	$205.60	$205.60	$205.60
Purchase #6	$78.91	13.672%	$89.6986	$89.70	$89.70	$89.70
Purchase #7	$65.44	11.705%	$73.0998	$73.10	$73.10	$73.10
7 purchase totals =	$840.61		$904.5311	$904.53	$904.50	$904.60