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	$40.55	7.234%	$43.4834	$43.48	$43.50	$43.50
Purchase #2	$30.68	13.863%	$34.9332	$34.93	$34.95	$34.90
Purchase #3	$157.40	10.747%	$174.3158	$174.32	$174.30	$174.30
Purchase #4	$142.51	4.339%	$148.6935	$148.69	$148.70	$148.70
Purchase #5	$65.69	10.465%	$72.5645	$72.56	$72.55	$72.60
Purchase #6	$10.76	3.286%	$11.1136	$11.11	$11.10	$11.10
Purchase #7	$105.31	3.503%	$108.999	$109.00	$109.00	$109.00
7 purchase totals =	$552.90		$594.1030	$594.09	$594.10	$594.10