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	$237.41	13.261%	$268.8929	$268.89	$268.90	$268.90
Purchase #2	$249.60	8.130%	$269.8925	$269.89	$269.90	$269.90
Purchase #3	$145.75	5.486%	$153.7458	$153.75	$153.75	$153.70
Purchase #4	$43.61	10.554%	$48.2126	$48.21	$48.20	$48.20
Purchase #5	$174.69	7.794%	$188.3053	$188.31	$188.30	$188.30
Purchase #6	$92.63	8.212%	$100.2368	$100.24	$100.25	$100.20
Purchase #7	$49.61	9.128%	$54.1384	$54.14	$54.15	$54.10
7 purchase totals =	$993.30		$1,083.4243	$1,083.43	$1,083.45	$1,083.30