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	$55.53	13.659%	$63.1148	$63.11	$63.10	$63.10
Purchase #2	$115.85	12.832%	$130.7159	$130.72	$130.70	$130.70
Purchase #3	$17.45	6.624%	$18.6059	$18.61	$18.60	$18.60
Purchase #4	$31.74	9.819%	$34.8566	$34.86	$34.85	$34.90
Purchase #5	$61.33	13.212%	$69.4329	$69.43	$69.45	$69.40
Purchase #6	$82.27	8.867%	$89.5649	$89.56	$89.55	$89.60
Purchase #7	$236.38	12.544%	$266.0315	$266.03	$266.05	$266.00
7 purchase totals =	$600.55		$672.3225	$672.32	$672.30	$672.30