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	$46.75	3.744%	$48.5003	$48.50	$48.50	$48.50
Purchase #2	$154.78	3.674%	$160.4666	$160.47	$160.45	$160.50
Purchase #3	$5.26	11.331%	$5.856	$5.86	$5.85	$5.90
Purchase #4	$224.82	10.738%	$248.9612	$248.96	$248.95	$249.00
Purchase #5	$172.67	4.532%	$180.4954	$180.50	$180.50	$180.50
Purchase #6	$161.25	13.153%	$182.4592	$182.46	$182.45	$182.50
Purchase #7	$241.66	13.291%	$273.779	$273.78	$273.80	$273.80
7 purchase totals =	$1,007.19		$1,100.5177	$1,100.53	$1,100.50	$1,100.70