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	$30.88	10.365%	$34.0807	$34.08	$34.10	$34.10
Purchase #2	$136.56	7.104%	$146.2612	$146.26	$146.25	$146.30
Purchase #3	$37.85	11.771%	$42.3053	$42.31	$42.30	$42.30
Purchase #4	$143.89	13.290%	$163.013	$163.01	$163.00	$163.00
Purchase #5	$31.36	3.295%	$32.3933	$32.39	$32.40	$32.40
Purchase #6	$99.40	9.179%	$108.5239	$108.52	$108.50	$108.50
Purchase #7	$120.90	6.328%	$128.5506	$128.55	$128.55	$128.60
7 purchase totals =	$600.84		$655.1280	$655.12	$655.10	$655.20