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	$66.67	5.586%	$70.3942	$70.39	$70.40	$70.40
Purchase #2	$184.50	3.156%	$190.3228	$190.32	$190.30	$190.30
Purchase #3	$215.81	6.353%	$229.5204	$229.52	$229.50	$229.50
Purchase #4	$175.64	8.562%	$190.6783	$190.68	$190.70	$190.70
Purchase #5	$54.37	12.473%	$61.1516	$61.15	$61.15	$61.20
Purchase #6	$117.67	6.838%	$125.7163	$125.72	$125.70	$125.70
Purchase #7	$112.56	10.709%	$124.6141	$124.61	$124.60	$124.60
7 purchase totals =	$927.22		$992.3977	$992.39	$992.35	$992.40