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	$75.30	10.566%	$83.2562	$83.26	$83.25	$83.30
Purchase #2	$72.52	7.128%	$77.6892	$77.69	$77.70	$77.70
Purchase #3	$219.68	10.151%	$241.9797	$241.98	$242.00	$242.00
Purchase #4	$159.41	9.665%	$174.817	$174.82	$174.80	$174.80
Purchase #5	$13.93	11.417%	$15.5204	$15.52	$15.50	$15.50
Purchase #6	$204.61	4.581%	$213.9832	$213.98	$214.00	$214.00
Purchase #7	$71.90	8.714%	$78.1654	$78.17	$78.15	$78.20
7 purchase totals =	$817.35		$885.4111	$885.42	$885.40	$885.50