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	$25.69	6.671%	$27.4038	$27.40	$27.40	$27.40
Purchase #2	$40.74	6.355%	$43.329	$43.33	$43.35	$43.30
Purchase #3	$159.33	8.446%	$172.787	$172.79	$172.80	$172.80
Purchase #4	$30.73	8.123%	$33.2262	$33.23	$33.25	$33.20
Purchase #5	$74.81	11.335%	$83.2897	$83.29	$83.30	$83.30
Purchase #6	$14.60	5.549%	$15.4102	$15.41	$15.40	$15.40
Purchase #7	$213.92	3.540%	$221.4928	$221.49	$221.50	$221.50
7 purchase totals =	$559.82		$596.9387	$596.94	$597.00	$596.90