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	$70.99	5.461%	$74.8668	$74.87	$74.85	$74.90
Purchase #2	$38.75	3.385%	$40.0617	$40.06	$40.05	$40.10
Purchase #3	$101.87	3.601%	$105.5383	$105.54	$105.55	$105.50
Purchase #4	$54.76	5.800%	$57.9361	$57.94	$57.95	$57.90
Purchase #5	$130.27	11.651%	$145.4478	$145.45	$145.45	$145.40
Purchase #6	$181.27	3.675%	$187.9317	$187.93	$187.95	$187.90
Purchase #7	$171.42	9.269%	$187.3089	$187.31	$187.30	$187.30
7 purchase totals =	$749.33		$799.0913	$799.10	$799.10	$799.00