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	$145.94	12.404%	$164.0424	$164.04	$164.05	$164.00
Purchase #2	$62.76	10.810%	$69.5444	$69.54	$69.55	$69.50
Purchase #3	$102.57	11.567%	$114.4343	$114.43	$114.45	$114.40
Purchase #4	$194.65	4.429%	$203.271	$203.27	$203.25	$203.30
Purchase #5	$5.52	13.764%	$6.2798	$6.28	$6.30	$6.30
Purchase #6	$78.37	3.192%	$80.8716	$80.87	$80.85	$80.90
Purchase #7	$11.51	11.404%	$12.8226	$12.82	$12.80	$12.80
7 purchase totals =	$601.32		$651.2661	$651.25	$651.25	$651.20