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	$40.57	6.820%	$43.3369	$43.34	$43.35	$43.30
Purchase #2	$62.37	6.603%	$66.4883	$66.49	$66.50	$66.50
Purchase #3	$81.82	4.718%	$85.6803	$85.68	$85.70	$85.70
Purchase #4	$77.27	8.216%	$83.6185	$83.62	$83.60	$83.60
Purchase #5	$127.90	8.347%	$138.5758	$138.58	$138.60	$138.60
Purchase #6	$22.79	12.114%	$25.5508	$25.55	$25.55	$25.60
Purchase #7	$94.65	6.502%	$100.8041	$100.80	$100.80	$100.80
7 purchase totals =	$507.37		$544.0547	$544.06	$544.10	$544.10