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	$241.52	3.578%	$250.1616	$250.16	$250.15	$250.20
Purchase #2	$208.71	9.874%	$229.318	$229.32	$229.30	$229.30
Purchase #3	$104.40	12.601%	$117.5554	$117.56	$117.55	$117.60
Purchase #4	$93.95	6.417%	$99.9788	$99.98	$100.00	$100.00
Purchase #5	$250.39	13.144%	$283.3013	$283.30	$283.30	$283.30
Purchase #6	$144.38	12.205%	$162.0016	$162.00	$162.00	$162.00
Purchase #7	$133.50	3.683%	$138.4168	$138.42	$138.40	$138.40
7 purchase totals =	$1,176.85		$1,280.7335	$1,280.74	$1,280.70	$1,280.80