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	$191.67	12.181%	$215.0173	$215.02	$215.00	$215.00
Purchase #2	$220.85	12.213%	$247.8224	$247.82	$247.80	$247.80
Purchase #3	$37.55	3.592%	$38.8988	$38.90	$38.90	$38.90
Purchase #4	$121.69	3.103%	$125.466	$125.47	$125.45	$125.50
Purchase #5	$132.58	8.301%	$143.5855	$143.59	$143.60	$143.60
Purchase #6	$6.51	4.751%	$6.8193	$6.82	$6.80	$6.80
Purchase #7	$77.47	6.834%	$82.7643	$82.76	$82.75	$82.80
7 purchase totals =	$788.32		$860.3736	$860.38	$860.30	$860.40