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	$59.63	3.327%	$61.6139	$61.61	$61.60	$61.60
Purchase #2	$171.88	13.220%	$194.6025	$194.60	$194.60	$194.60
Purchase #3	$155.77	8.467%	$168.959	$168.96	$168.95	$169.00
Purchase #4	$185.63	10.794%	$205.6669	$205.67	$205.65	$205.70
Purchase #5	$143.95	11.717%	$160.8166	$160.82	$160.80	$160.80
Purchase #6	$246.53	13.438%	$279.6587	$279.66	$279.65	$279.70
Purchase #7	$52.31	7.611%	$56.2913	$56.29	$56.30	$56.30
7 purchase totals =	$1,015.70		$1,127.6089	$1,127.61	$1,127.55	$1,127.70