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	$180.29	3.730%	$187.0148	$187.01	$187.00	$187.00
Purchase #2	$222.84	12.756%	$251.2655	$251.27	$251.25	$251.30
Purchase #3	$62.44	6.456%	$66.4711	$66.47	$66.45	$66.50
Purchase #4	$200.42	8.168%	$216.7903	$216.79	$216.80	$216.80
Purchase #5	$114.31	8.432%	$123.9486	$123.95	$123.95	$123.90
Purchase #6	$19.81	3.240%	$20.4518	$20.45	$20.45	$20.50
Purchase #7	$205.76	8.662%	$223.5829	$223.58	$223.60	$223.60
7 purchase totals =	$1,005.87		$1,089.5250	$1,089.52	$1,089.50	$1,089.60