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	$112.89	9.197%	$123.2725	$123.27	$123.25	$123.30
Purchase #2	$236.81	5.705%	$250.32	$250.32	$250.30	$250.30
Purchase #3	$6.95	13.413%	$7.8822	$7.88	$7.90	$7.90
Purchase #4	$108.61	8.706%	$118.0656	$118.07	$118.05	$118.10
Purchase #5	$61.85	6.852%	$66.088	$66.09	$66.10	$66.10
Purchase #6	$153.29	13.810%	$174.4593	$174.46	$174.45	$174.50
Purchase #7	$141.32	8.513%	$153.3506	$153.35	$153.35	$153.40
7 purchase totals =	$821.72		$893.4382	$893.44	$893.40	$893.60