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	$205.53	4.174%	$214.1088	$214.11	$214.10	$214.10
Purchase #2	$36.85	9.858%	$40.4827	$40.48	$40.50	$40.50
Purchase #3	$124.50	12.666%	$140.2692	$140.27	$140.25	$140.30
Purchase #4	$21.60	5.609%	$22.8115	$22.81	$22.80	$22.80
Purchase #5	$15.52	11.545%	$17.3118	$17.31	$17.30	$17.30
Purchase #6	$38.59	3.304%	$39.865	$39.87	$39.85	$39.90
Purchase #7	$59.81	9.847%	$65.6995	$65.70	$65.70	$65.70
7 purchase totals =	$502.40		$540.5485	$540.55	$540.50	$540.60