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	$171.57	7.515%	$184.4635	$184.46	$184.45	$184.50
Purchase #2	$93.75	9.357%	$102.5222	$102.52	$102.50	$102.50
Purchase #3	$94.59	4.797%	$99.1275	$99.13	$99.15	$99.10
Purchase #4	$76.59	3.708%	$79.43	$79.43	$79.45	$79.40
Purchase #5	$43.44	7.536%	$46.7136	$46.71	$46.70	$46.70
Purchase #6	$230.73	10.802%	$255.6535	$255.65	$255.65	$255.70
Purchase #7	$26.29	9.725%	$28.8467	$28.85	$28.85	$28.80
7 purchase totals =	$736.96		$796.7570	$796.75	$796.75	$796.70