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	$56.40	6.319%	$59.9639	$59.96	$59.95	$60.00
Purchase #2	$31.73	10.409%	$35.0328	$35.03	$35.05	$35.00
Purchase #3	$50.40	6.814%	$53.8343	$53.83	$53.85	$53.80
Purchase #4	$190.86	12.548%	$214.8091	$214.81	$214.80	$214.80
Purchase #5	$72.64	8.595%	$78.8834	$78.88	$78.90	$78.90
Purchase #6	$242.90	3.684%	$251.8484	$251.85	$251.85	$251.80
Purchase #7	$42.48	13.653%	$48.2798	$48.28	$48.30	$48.30
7 purchase totals =	$687.41		$742.6517	$742.64	$742.70	$742.60