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	$9.41	9.647%	$10.3178	$10.32	$10.30	$10.30
Purchase #2	$45.39	12.625%	$51.1205	$51.12	$51.10	$51.10
Purchase #3	$152.45	13.666%	$173.2838	$173.28	$173.30	$173.30
Purchase #4	$68.28	13.144%	$77.2547	$77.25	$77.25	$77.30
Purchase #5	$227.33	12.717%	$256.2396	$256.24	$256.25	$256.20
Purchase #6	$98.51	13.491%	$111.8	$111.80	$111.80	$111.80
Purchase #7	$67.49	5.320%	$71.0805	$71.08	$71.10	$71.10
7 purchase totals =	$668.86		$751.0969	$751.09	$751.10	$751.10