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	$26.69	9.217%	$29.15	$29.15	$29.15	$29.20
Purchase #2	$205.91	3.253%	$212.6083	$212.61	$212.60	$212.60
Purchase #3	$95.29	8.659%	$103.5412	$103.54	$103.55	$103.50
Purchase #4	$47.47	7.799%	$51.1722	$51.17	$51.15	$51.20
Purchase #5	$82.70	13.860%	$94.1622	$94.16	$94.15	$94.20
Purchase #6	$193.92	13.388%	$219.882	$219.88	$219.90	$219.90
Purchase #7	$83.72	9.824%	$91.9447	$91.94	$91.95	$91.90
7 purchase totals =	$735.70		$802.4606	$802.45	$802.45	$802.50