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	$139.63	9.402%	$152.758	$152.76	$152.75	$152.80
Purchase #2	$166.42	4.200%	$173.4096	$173.41	$173.40	$173.40
Purchase #3	$37.68	3.339%	$38.9381	$38.94	$38.95	$38.90
Purchase #4	$66.28	13.368%	$75.1403	$75.14	$75.15	$75.10
Purchase #5	$240.34	3.728%	$249.2999	$249.30	$249.30	$249.30
Purchase #6	$172.95	8.217%	$187.1613	$187.16	$187.15	$187.20
Purchase #7	$197.52	13.223%	$223.6381	$223.64	$223.65	$223.60
7 purchase totals =	$1,020.82		$1,100.3453	$1,100.35	$1,100.35	$1,100.30