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	$55.88	11.866%	$62.5107	$62.51	$62.50	$62.50
Purchase #2	$153.37	4.214%	$159.833	$159.83	$159.85	$159.80
Purchase #3	$27.54	13.783%	$31.3358	$31.34	$31.35	$31.30
Purchase #4	$25.33	8.321%	$27.4377	$27.44	$27.45	$27.40
Purchase #5	$47.46	12.527%	$53.4053	$53.41	$53.40	$53.40
Purchase #6	$10.86	12.726%	$12.242	$12.24	$12.25	$12.20
Purchase #7	$44.57	10.651%	$49.3172	$49.32	$49.30	$49.30
7 purchase totals =	$365.01		$396.0817	$396.09	$396.10	$395.90