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	$34.37	6.660%	$36.659	$36.66	$36.65	$36.70
Purchase #2	$152.89	3.406%	$158.0974	$158.10	$158.10	$158.10
Purchase #3	$40.26	8.735%	$43.7767	$43.78	$43.80	$43.80
Purchase #4	$211.67	6.477%	$225.3799	$225.38	$225.40	$225.40
Purchase #5	$93.87	12.118%	$105.2452	$105.25	$105.25	$105.20
Purchase #6	$193.28	13.290%	$218.9669	$218.97	$218.95	$219.00
Purchase #7	$181.69	4.696%	$190.2222	$190.22	$190.20	$190.20
7 purchase totals =	$908.03		$978.3473	$978.36	$978.35	$978.40