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	$174.81	6.127%	$185.5206	$185.52	$185.50	$185.50
Purchase #2	$81.78	7.579%	$87.9781	$87.98	$88.00	$88.00
Purchase #3	$123.83	11.797%	$138.4382	$138.44	$138.45	$138.40
Purchase #4	$83.58	6.864%	$89.3169	$89.32	$89.30	$89.30
Purchase #5	$224.43	10.434%	$247.847	$247.85	$247.85	$247.80
Purchase #6	$52.45	10.669%	$58.0459	$58.05	$58.05	$58.00
Purchase #7	$75.93	8.278%	$82.2155	$82.22	$82.20	$82.20
7 purchase totals =	$816.81		$889.3622	$889.38	$889.35	$889.20