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	$49.95	13.363%	$56.6248	$56.62	$56.60	$56.60
Purchase #2	$171.52	6.865%	$183.2948	$183.29	$183.30	$183.30
Purchase #3	$162.40	6.224%	$172.5078	$172.51	$172.50	$172.50
Purchase #4	$99.91	4.319%	$104.2251	$104.23	$104.25	$104.20
Purchase #5	$65.52	5.360%	$69.0319	$69.03	$69.05	$69.00
Purchase #6	$28.89	7.726%	$31.122	$31.12	$31.10	$31.10
Purchase #7	$30.63	7.376%	$32.8893	$32.89	$32.90	$32.90
7 purchase totals =	$608.82		$649.6957	$649.69	$649.70	$649.60