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	$142.75	8.791%	$155.2992	$155.30	$155.30	$155.30
Purchase #2	$142.52	7.855%	$153.7149	$153.71	$153.70	$153.70
Purchase #3	$130.74	10.396%	$144.3317	$144.33	$144.35	$144.30
Purchase #4	$28.95	11.865%	$32.3849	$32.38	$32.40	$32.40
Purchase #5	$112.46	13.390%	$127.5184	$127.52	$127.50	$127.50
Purchase #6	$183.73	7.155%	$196.8759	$196.88	$196.90	$196.90
Purchase #7	$197.54	5.497%	$208.3988	$208.40	$208.40	$208.40
7 purchase totals =	$938.69		$1,018.5238	$1,018.52	$1,018.55	$1,018.50