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	$60.72	6.146%	$64.4519	$64.45	$64.45	$64.50
Purchase #2	$175.65	12.767%	$198.0752	$198.08	$198.10	$198.10
Purchase #3	$32.47	12.195%	$36.4297	$36.43	$36.45	$36.40
Purchase #4	$208.42	8.470%	$226.0732	$226.07	$226.05	$226.10
Purchase #5	$130.89	9.506%	$143.3324	$143.33	$143.35	$143.30
Purchase #6	$190.65	3.115%	$196.5887	$196.59	$196.60	$196.60
Purchase #7	$74.56	8.517%	$80.9103	$80.91	$80.90	$80.90
7 purchase totals =	$873.36		$945.8614	$945.86	$945.90	$945.90