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	$120.46	10.291%	$132.8565	$132.86	$132.85	$132.90
Purchase #2	$35.93	13.259%	$40.694	$40.69	$40.70	$40.70
Purchase #3	$158.58	8.694%	$172.3669	$172.37	$172.35	$172.40
Purchase #4	$136.30	11.362%	$151.7864	$151.79	$151.80	$151.80
Purchase #5	$87.75	4.550%	$91.7426	$91.74	$91.75	$91.70
Purchase #6	$136.35	13.348%	$154.55	$154.55	$154.55	$154.60
Purchase #7	$101.39	8.311%	$109.8165	$109.82	$109.80	$109.80
7 purchase totals =	$776.76		$853.8129	$853.82	$853.80	$853.90