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	$172.39	10.436%	$190.3806	$190.38	$190.40	$190.40
Purchase #2	$234.56	7.776%	$252.7994	$252.80	$252.80	$252.80
Purchase #3	$161.37	6.787%	$172.3222	$172.32	$172.30	$172.30
Purchase #4	$127.32	3.676%	$132.0003	$132.00	$132.00	$132.00
Purchase #5	$46.98	6.511%	$50.0389	$50.04	$50.05	$50.00
Purchase #6	$120.92	12.596%	$136.1511	$136.15	$136.15	$136.20
Purchase #7	$40.93	4.857%	$42.918	$42.92	$42.90	$42.90
7 purchase totals =	$904.47		$976.6105	$976.61	$976.60	$976.60