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	$38.55	9.151%	$42.0777	$42.08	$42.10	$42.10
Purchase #2	$203.96	8.654%	$221.6107	$221.61	$221.60	$221.60
Purchase #3	$47.52	9.809%	$52.1812	$52.18	$52.20	$52.20
Purchase #4	$40.71	6.850%	$43.4986	$43.50	$43.50	$43.50
Purchase #5	$184.30	13.339%	$208.8838	$208.88	$208.90	$208.90
Purchase #6	$120.94	11.125%	$134.3946	$134.39	$134.40	$134.40
Purchase #7	$216.54	11.142%	$240.6669	$240.67	$240.65	$240.70
7 purchase totals =	$852.52		$943.3135	$943.31	$943.35	$943.40