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	$81.41	11.819%	$91.0318	$91.03	$91.05	$91.00
Purchase #2	$105.56	13.182%	$119.4749	$119.47	$119.45	$119.50
Purchase #3	$239.49	6.858%	$255.9142	$255.91	$255.90	$255.90
Purchase #4	$94.72	3.599%	$98.129	$98.13	$98.15	$98.10
Purchase #5	$54.26	9.258%	$59.2834	$59.28	$59.30	$59.30
Purchase #6	$20.91	13.634%	$23.7609	$23.76	$23.75	$23.80
Purchase #7	$165.89	6.663%	$176.9433	$176.94	$176.95	$176.90
7 purchase totals =	$762.24		$824.5375	$824.52	$824.55	$824.50