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	$160.97	6.521%	$171.4669	$171.47	$171.45	$171.50
Purchase #2	$140.62	8.259%	$152.2338	$152.23	$152.25	$152.20
Purchase #3	$108.57	9.447%	$118.8266	$118.83	$118.85	$118.80
Purchase #4	$228.57	4.167%	$238.0945	$238.09	$238.10	$238.10
Purchase #5	$91.27	9.133%	$99.6057	$99.61	$99.60	$99.60
Purchase #6	$205.56	13.656%	$233.6313	$233.63	$233.65	$233.60
Purchase #7	$62.32	5.505%	$65.7507	$65.75	$65.75	$65.80
7 purchase totals =	$997.88		$1,079.6095	$1,079.61	$1,079.65	$1,079.60