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	$40.73	11.798%	$45.5353	$45.54	$45.55	$45.50
Purchase #2	$44.50	5.185%	$46.8073	$46.81	$46.80	$46.80
Purchase #3	$54.28	5.799%	$57.4277	$57.43	$57.45	$57.40
Purchase #4	$246.66	4.376%	$257.4538	$257.45	$257.45	$257.50
Purchase #5	$167.46	10.353%	$184.7971	$184.80	$184.80	$184.80
Purchase #6	$211.78	4.361%	$221.0157	$221.02	$221.00	$221.00
Purchase #7	$225.46	13.114%	$255.0268	$255.03	$255.05	$255.00
7 purchase totals =	$990.87		$1,068.0637	$1,068.08	$1,068.10	$1,068.00