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	$38.25	5.344%	$40.2941	$40.29	$40.30	$40.30
Purchase #2	$70.72	8.679%	$76.8578	$76.86	$76.85	$76.90
Purchase #3	$115.56	10.139%	$127.2766	$127.28	$127.30	$127.30
Purchase #4	$52.30	5.711%	$55.2869	$55.29	$55.30	$55.30
Purchase #5	$200.91	3.185%	$207.309	$207.31	$207.30	$207.30
Purchase #6	$103.39	4.763%	$108.3145	$108.31	$108.30	$108.30
Purchase #7	$193.26	9.188%	$211.0167	$211.02	$211.00	$211.00
7 purchase totals =	$774.39		$826.3556	$826.36	$826.35	$826.40