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	$98.79	6.627%	$105.3368	$105.34	$105.35	$105.30
Purchase #2	$247.86	12.728%	$279.4076	$279.41	$279.40	$279.40
Purchase #3	$233.53	5.530%	$246.4442	$246.44	$246.45	$246.40
Purchase #4	$78.80	12.763%	$88.8572	$88.86	$88.85	$88.90
Purchase #5	$101.70	7.236%	$109.059	$109.06	$109.05	$109.10
Purchase #6	$145.73	6.116%	$154.6428	$154.64	$154.65	$154.60
Purchase #7	$90.75	9.113%	$99.02	$99.02	$99.00	$99.00
7 purchase totals =	$997.16		$1,082.7676	$1,082.77	$1,082.75	$1,082.70