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	$199.38	4.774%	$208.8984	$208.90	$208.90	$208.90
Purchase #2	$173.88	7.667%	$187.2114	$187.21	$187.20	$187.20
Purchase #3	$33.28	12.578%	$37.466	$37.47	$37.45	$37.50
Purchase #4	$38.68	10.445%	$42.7201	$42.72	$42.70	$42.70
Purchase #5	$78.93	7.870%	$85.1418	$85.14	$85.15	$85.10
Purchase #6	$120.28	12.168%	$134.9157	$134.92	$134.90	$134.90
Purchase #7	$128.74	12.864%	$145.3011	$145.30	$145.30	$145.30
7 purchase totals =	$773.17		$841.6545	$841.66	$841.60	$841.60