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	$74.79	5.494%	$78.899	$78.90	$78.90	$78.90
Purchase #2	$143.43	10.271%	$158.1617	$158.16	$158.15	$158.20
Purchase #3	$73.54	5.294%	$77.4332	$77.43	$77.45	$77.40
Purchase #4	$237.86	8.642%	$258.4159	$258.42	$258.40	$258.40
Purchase #5	$136.97	9.675%	$150.2218	$150.22	$150.20	$150.20
Purchase #6	$147.93	4.194%	$154.1342	$154.13	$154.15	$154.10
Purchase #7	$162.72	10.177%	$179.28	$179.28	$179.30	$179.30
7 purchase totals =	$977.24		$1,056.5458	$1,056.54	$1,056.55	$1,056.50