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	$153.88	12.415%	$172.9842	$172.98	$173.00	$173.00
Purchase #2	$156.36	11.129%	$173.7613	$173.76	$173.75	$173.80
Purchase #3	$21.89	7.279%	$23.4834	$23.48	$23.50	$23.50
Purchase #4	$92.93	7.558%	$99.9536	$99.95	$99.95	$100.00
Purchase #5	$117.29	5.110%	$123.2835	$123.28	$123.30	$123.30
Purchase #6	$99.50	10.188%	$109.6371	$109.64	$109.65	$109.60
Purchase #7	$218.71	13.527%	$248.2949	$248.29	$248.30	$248.30
7 purchase totals =	$860.56		$951.3980	$951.38	$951.45	$951.50