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	$76.51	6.506%	$81.4877	$81.49	$81.50	$81.50
Purchase #2	$61.27	6.138%	$65.0308	$65.03	$65.05	$65.00
Purchase #3	$82.31	5.858%	$87.1317	$87.13	$87.15	$87.10
Purchase #4	$188.88	4.247%	$196.9017	$196.90	$196.90	$196.90
Purchase #5	$223.49	9.229%	$244.1159	$244.12	$244.10	$244.10
Purchase #6	$32.76	13.804%	$37.2822	$37.28	$37.30	$37.30
Purchase #7	$81.60	8.520%	$88.5523	$88.55	$88.55	$88.60
7 purchase totals =	$746.82		$800.5023	$800.50	$800.55	$800.50