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	$52.70	13.543%	$59.8372	$59.84	$59.85	$59.80
Purchase #2	$129.81	12.175%	$145.6144	$145.61	$145.60	$145.60
Purchase #3	$197.82	9.383%	$216.3815	$216.38	$216.40	$216.40
Purchase #4	$211.33	7.701%	$227.6045	$227.60	$227.60	$227.60
Purchase #5	$111.47	6.217%	$118.4001	$118.40	$118.40	$118.40
Purchase #6	$74.27	5.403%	$78.2828	$78.28	$78.30	$78.30
Purchase #7	$18.42	6.750%	$19.6634	$19.66	$19.65	$19.70
7 purchase totals =	$795.82		$865.7839	$865.77	$865.80	$865.80