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	$43.91	11.704%	$49.0492	$49.05	$49.05	$49.00
Purchase #2	$200.91	4.744%	$210.4412	$210.44	$210.45	$210.40
Purchase #3	$88.29	13.594%	$100.2921	$100.29	$100.30	$100.30
Purchase #4	$146.60	10.634%	$162.1894	$162.19	$162.20	$162.20
Purchase #5	$127.82	9.322%	$139.7354	$139.74	$139.75	$139.70
Purchase #6	$119.53	6.423%	$127.2074	$127.21	$127.20	$127.20
Purchase #7	$117.70	11.758%	$131.5392	$131.54	$131.55	$131.50
7 purchase totals =	$844.76		$920.4539	$920.46	$920.50	$920.30