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	$48.38	6.359%	$51.4565	$51.46	$51.45	$51.50
Purchase #2	$151.50	7.159%	$162.3459	$162.35	$162.35	$162.30
Purchase #3	$150.36	13.419%	$170.5368	$170.54	$170.55	$170.50
Purchase #4	$73.93	6.438%	$78.6896	$78.69	$78.70	$78.70
Purchase #5	$86.35	3.176%	$89.0925	$89.09	$89.10	$89.10
Purchase #6	$154.36	3.838%	$160.2843	$160.28	$160.30	$160.30
Purchase #7	$40.44	4.324%	$42.1886	$42.19	$42.20	$42.20
7 purchase totals =	$705.32		$754.5942	$754.60	$754.65	$754.60