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	$11.54	11.667%	$12.8864	$12.89	$12.90	$12.90
Purchase #2	$62.54	13.258%	$70.8316	$70.83	$70.85	$70.80
Purchase #3	$169.99	11.282%	$189.1683	$189.17	$189.15	$189.20
Purchase #4	$149.28	10.209%	$164.52	$164.52	$164.50	$164.50
Purchase #5	$146.44	10.324%	$161.5585	$161.56	$161.55	$161.60
Purchase #6	$127.52	12.535%	$143.5046	$143.50	$143.50	$143.50
Purchase #7	$193.45	11.592%	$215.8747	$215.87	$215.85	$215.90
7 purchase totals =	$860.76		$958.3441	$958.34	$958.30	$958.40