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	$38.70	9.788%	$42.488	$42.49	$42.50	$42.50
Purchase #2	$20.27	11.118%	$22.5236	$22.52	$22.50	$22.50
Purchase #3	$99.91	10.470%	$110.3706	$110.37	$110.35	$110.40
Purchase #4	$103.52	9.272%	$113.1184	$113.12	$113.10	$113.10
Purchase #5	$48.57	11.310%	$54.0633	$54.06	$54.05	$54.10
Purchase #6	$124.37	6.620%	$132.6033	$132.60	$132.60	$132.60
Purchase #7	$115.95	13.316%	$131.3899	$131.39	$131.40	$131.40
7 purchase totals =	$551.29		$606.5571	$606.55	$606.50	$606.60