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	$56.42	5.815%	$59.7008	$59.70	$59.70	$59.70
Purchase #2	$147.37	4.814%	$154.4644	$154.46	$154.45	$154.50
Purchase #3	$180.29	13.122%	$203.9477	$203.95	$203.95	$203.90
Purchase #4	$54.69	10.491%	$60.4275	$60.43	$60.45	$60.40
Purchase #5	$140.26	8.690%	$152.4486	$152.45	$152.45	$152.40
Purchase #6	$234.28	13.174%	$265.144	$265.14	$265.15	$265.10
Purchase #7	$99.29	5.839%	$105.0875	$105.09	$105.10	$105.10
7 purchase totals =	$912.60		$1,001.2205	$1,001.22	$1,001.25	$1,001.10