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	$82.98	9.438%	$90.8117	$90.81	$90.80	$90.80
Purchase #2	$213.69	8.253%	$231.3258	$231.33	$231.35	$231.30
Purchase #3	$216.46	3.211%	$223.4105	$223.41	$223.40	$223.40
Purchase #4	$151.50	12.488%	$170.4193	$170.42	$170.40	$170.40
Purchase #5	$243.96	12.748%	$275.06	$275.06	$275.05	$275.10
Purchase #6	$143.42	13.720%	$163.0972	$163.10	$163.10	$163.10
Purchase #7	$113.76	11.776%	$127.1564	$127.16	$127.15	$127.20
7 purchase totals =	$1,165.77		$1,281.2809	$1,281.29	$1,281.25	$1,281.30