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	$133.34	11.845%	$149.1341	$149.13	$149.15	$149.10
Purchase #2	$237.27	7.579%	$255.2527	$255.25	$255.25	$255.30
Purchase #3	$158.83	8.382%	$172.1431	$172.14	$172.15	$172.10
Purchase #4	$12.82	4.826%	$13.4387	$13.44	$13.45	$13.40
Purchase #5	$161.25	6.675%	$172.0134	$172.01	$172.00	$172.00
Purchase #6	$153.61	11.782%	$171.7083	$171.71	$171.70	$171.70
Purchase #7	$157.92	7.592%	$169.9093	$169.91	$169.90	$169.90
7 purchase totals =	$1,015.04		$1,103.5996	$1,103.59	$1,103.60	$1,103.50