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	$231.61	4.541%	$242.1274	$242.13	$242.15	$242.10
Purchase #2	$182.33	5.556%	$192.4603	$192.46	$192.45	$192.50
Purchase #3	$61.75	10.476%	$68.2189	$68.22	$68.20	$68.20
Purchase #4	$29.42	13.420%	$33.3682	$33.37	$33.35	$33.40
Purchase #5	$79.65	3.598%	$82.5158	$82.52	$82.50	$82.50
Purchase #6	$65.80	10.819%	$72.9189	$72.92	$72.90	$72.90
Purchase #7	$35.68	13.136%	$40.3669	$40.37	$40.35	$40.40
7 purchase totals =	$686.24		$731.9764	$731.99	$731.90	$732.00