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	$142.34	11.366%	$158.5184	$158.52	$158.50	$158.50
Purchase #2	$55.72	5.813%	$58.959	$58.96	$58.95	$59.00
Purchase #3	$233.78	6.493%	$248.9593	$248.96	$248.95	$249.00
Purchase #4	$137.52	11.314%	$153.079	$153.08	$153.10	$153.10
Purchase #5	$70.58	8.752%	$76.7572	$76.76	$76.75	$76.80
Purchase #6	$171.67	9.536%	$188.0405	$188.04	$188.05	$188.00
Purchase #7	$104.95	6.432%	$111.7004	$111.70	$111.70	$111.70
7 purchase totals =	$916.56		$996.0138	$996.02	$996.00	$996.10