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	$91.97	8.334%	$99.6348	$99.63	$99.65	$99.60
Purchase #2	$94.38	4.278%	$98.4176	$98.42	$98.40	$98.40
Purchase #3	$239.37	6.789%	$255.6208	$255.62	$255.60	$255.60
Purchase #4	$207.62	7.390%	$222.9631	$222.96	$222.95	$223.00
Purchase #5	$249.72	9.857%	$274.3349	$274.33	$274.35	$274.30
Purchase #6	$37.66	11.219%	$41.8851	$41.89	$41.90	$41.90
Purchase #7	$237.84	7.255%	$255.0953	$255.10	$255.10	$255.10
7 purchase totals =	$1,158.56		$1,247.9516	$1,247.95	$1,247.95	$1,247.90