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	$37.71	13.395%	$42.7613	$42.76	$42.75	$42.80
Purchase #2	$243.30	11.764%	$271.9218	$271.92	$271.90	$271.90
Purchase #3	$97.82	7.512%	$105.1682	$105.17	$105.15	$105.20
Purchase #4	$182.61	5.591%	$192.8197	$192.82	$192.80	$192.80
Purchase #5	$127.29	13.406%	$144.3545	$144.35	$144.35	$144.40
Purchase #6	$42.39	5.433%	$44.693	$44.69	$44.70	$44.70
Purchase #7	$215.76	11.258%	$240.0503	$240.05	$240.05	$240.10
7 purchase totals =	$946.88		$1,041.7688	$1,041.76	$1,041.70	$1,041.90