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	$150.82	13.509%	$171.1943	$171.19	$171.20	$171.20
Purchase #2	$152.91	13.339%	$173.3067	$173.31	$173.30	$173.30
Purchase #3	$92.47	9.526%	$101.2787	$101.28	$101.30	$101.30
Purchase #4	$60.58	6.586%	$64.5698	$64.57	$64.55	$64.60
Purchase #5	$230.27	3.593%	$238.5436	$238.54	$238.55	$238.50
Purchase #6	$173.97	13.618%	$197.6612	$197.66	$197.65	$197.70
Purchase #7	$72.84	8.102%	$78.7415	$78.74	$78.75	$78.70
7 purchase totals =	$933.86		$1,025.2958	$1,025.29	$1,025.30	$1,025.30