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	$121.93	4.572%	$127.5046	$127.50	$127.50	$127.50
Purchase #2	$130.56	12.404%	$146.7547	$146.75	$146.75	$146.80
Purchase #3	$222.83	11.245%	$247.8872	$247.89	$247.90	$247.90
Purchase #4	$49.68	5.806%	$52.5644	$52.56	$52.55	$52.60
Purchase #5	$43.94	6.705%	$46.8862	$46.89	$46.90	$46.90
Purchase #6	$65.62	6.691%	$70.0106	$70.01	$70.00	$70.00
Purchase #7	$93.72	5.867%	$99.2186	$99.22	$99.20	$99.20
7 purchase totals =	$728.28		$790.8263	$790.82	$790.80	$790.90