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	$175.27	7.572%	$188.5414	$188.54	$188.55	$188.50
Purchase #2	$62.45	3.867%	$64.8649	$64.86	$64.85	$64.90
Purchase #3	$165.85	12.112%	$185.9378	$185.94	$185.95	$185.90
Purchase #4	$204.33	9.240%	$223.2101	$223.21	$223.20	$223.20
Purchase #5	$35.29	5.137%	$37.1028	$37.10	$37.10	$37.10
Purchase #6	$24.75	12.491%	$27.8415	$27.84	$27.85	$27.80
Purchase #7	$14.99	6.495%	$15.9636	$15.96	$15.95	$16.00
7 purchase totals =	$682.93		$743.4621	$743.45	$743.45	$743.40