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	$64.68	11.515%	$72.1279	$72.13	$72.15	$72.10
Purchase #2	$197.32	7.672%	$212.4584	$212.46	$212.45	$212.50
Purchase #3	$34.82	10.306%	$38.4085	$38.41	$38.40	$38.40
Purchase #4	$89.58	10.606%	$99.0809	$99.08	$99.10	$99.10
Purchase #5	$189.81	11.332%	$211.3193	$211.32	$211.30	$211.30
Purchase #6	$114.98	10.540%	$127.0989	$127.10	$127.10	$127.10
Purchase #7	$194.63	9.487%	$213.0945	$213.09	$213.10	$213.10
7 purchase totals =	$885.82		$973.5884	$973.59	$973.60	$973.60