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	$92.85	7.781%	$100.0747	$100.07	$100.05	$100.10
Purchase #2	$137.89	4.807%	$144.5184	$144.52	$144.50	$144.50
Purchase #3	$195.71	5.824%	$207.1082	$207.11	$207.10	$207.10
Purchase #4	$166.58	10.687%	$184.3824	$184.38	$184.40	$184.40
Purchase #5	$221.52	5.530%	$233.7701	$233.77	$233.75	$233.80
Purchase #6	$79.70	7.501%	$85.6783	$85.68	$85.70	$85.70
Purchase #7	$19.54	3.271%	$20.1792	$20.18	$20.20	$20.20
7 purchase totals =	$913.79		$975.7113	$975.71	$975.70	$975.80