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	$248.27	11.130%	$275.9025	$275.90	$275.90	$275.90
Purchase #2	$64.66	5.412%	$68.1594	$68.16	$68.15	$68.20
Purchase #3	$81.39	11.223%	$90.5244	$90.52	$90.50	$90.50
Purchase #4	$186.57	11.434%	$207.9024	$207.90	$207.90	$207.90
Purchase #5	$24.45	11.539%	$27.2713	$27.27	$27.25	$27.30
Purchase #6	$27.49	6.331%	$29.2304	$29.23	$29.25	$29.20
Purchase #7	$218.60	10.539%	$241.6383	$241.64	$241.65	$241.60
7 purchase totals =	$851.43		$940.6287	$940.62	$940.60	$940.60