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	$245.47	13.852%	$279.4725	$279.47	$279.45	$279.50
Purchase #2	$62.71	11.390%	$69.8527	$69.85	$69.85	$69.90
Purchase #3	$146.93	4.137%	$153.0085	$153.01	$153.00	$153.00
Purchase #4	$209.56	13.463%	$237.7731	$237.77	$237.75	$237.80
Purchase #5	$151.46	4.559%	$158.3651	$158.37	$158.35	$158.40
Purchase #6	$57.43	4.561%	$60.0494	$60.05	$60.05	$60.00
Purchase #7	$190.76	13.697%	$216.8884	$216.89	$216.90	$216.90
7 purchase totals =	$1,064.32		$1,175.4097	$1,175.41	$1,175.35	$1,175.50