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	$21.64	12.670%	$24.3818	$24.38	$24.40	$24.40
Purchase #2	$136.48	7.443%	$146.6382	$146.64	$146.65	$146.60
Purchase #3	$78.37	11.131%	$87.0934	$87.09	$87.10	$87.10
Purchase #4	$57.66	11.553%	$64.3215	$64.32	$64.30	$64.30
Purchase #5	$81.89	9.640%	$89.7842	$89.78	$89.80	$89.80
Purchase #6	$99.79	6.167%	$105.944	$105.94	$105.95	$105.90
Purchase #7	$237.45	4.679%	$248.5603	$248.56	$248.55	$248.60
7 purchase totals =	$713.28		$766.7234	$766.71	$766.75	$766.70