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	$52.81	12.796%	$59.5676	$59.57	$59.55	$59.60
Purchase #2	$235.94	3.531%	$244.271	$244.27	$244.25	$244.30
Purchase #3	$121.37	10.108%	$133.6381	$133.64	$133.65	$133.60
Purchase #4	$135.74	13.719%	$154.3622	$154.36	$154.35	$154.40
Purchase #5	$76.42	7.521%	$82.1675	$82.17	$82.15	$82.20
Purchase #6	$35.88	9.526%	$39.2979	$39.30	$39.30	$39.30
Purchase #7	$228.27	4.278%	$238.0354	$238.04	$238.05	$238.00
7 purchase totals =	$886.43		$951.3397	$951.35	$951.30	$951.40