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	$29.44	12.752%	$33.1942	$33.19	$33.20	$33.20
Purchase #2	$134.66	4.472%	$140.682	$140.68	$140.70	$140.70
Purchase #3	$214.81	4.259%	$223.9588	$223.96	$223.95	$224.00
Purchase #4	$130.54	10.335%	$144.0313	$144.03	$144.05	$144.00
Purchase #5	$240.66	6.180%	$255.5328	$255.53	$255.55	$255.50
Purchase #6	$94.91	5.221%	$99.8653	$99.87	$99.85	$99.90
Purchase #7	$240.30	11.633%	$268.2541	$268.25	$268.25	$268.30
7 purchase totals =	$1,085.32		$1,165.5185	$1,165.51	$1,165.55	$1,165.60