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	$15.79	5.831%	$16.7107	$16.71	$16.70	$16.70
Purchase #2	$100.36	10.727%	$111.1256	$111.13	$111.15	$111.10
Purchase #3	$134.72	4.332%	$140.5561	$140.56	$140.55	$140.60
Purchase #4	$109.85	6.535%	$117.0287	$117.03	$117.05	$117.00
Purchase #5	$157.61	11.573%	$175.8502	$175.85	$175.85	$175.90
Purchase #6	$171.27	4.414%	$178.8299	$178.83	$178.85	$178.80
Purchase #7	$195.41	10.751%	$216.4185	$216.42	$216.40	$216.40
7 purchase totals =	$885.01		$956.5197	$956.53	$956.55	$956.50