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	$161.66	10.612%	$178.8154	$178.82	$178.80	$178.80
Purchase #2	$25.90	7.864%	$27.9368	$27.94	$27.95	$27.90
Purchase #3	$105.73	5.859%	$111.9247	$111.92	$111.90	$111.90
Purchase #4	$22.74	12.575%	$25.5996	$25.60	$25.60	$25.60
Purchase #5	$9.26	12.850%	$10.4499	$10.45	$10.45	$10.40
Purchase #6	$65.37	3.311%	$67.5344	$67.53	$67.55	$67.50
Purchase #7	$102.64	11.708%	$114.6571	$114.66	$114.65	$114.70
7 purchase totals =	$493.30		$536.9179	$536.92	$536.90	$536.80