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	$239.27	13.213%	$270.8847	$270.88	$270.90	$270.90
Purchase #2	$165.69	9.775%	$181.8862	$181.89	$181.90	$181.90
Purchase #3	$238.78	4.473%	$249.4606	$249.46	$249.45	$249.50
Purchase #4	$181.88	9.828%	$199.7552	$199.76	$199.75	$199.80
Purchase #5	$46.88	11.160%	$52.1118	$52.11	$52.10	$52.10
Purchase #6	$228.78	5.693%	$241.8044	$241.80	$241.80	$241.80
Purchase #7	$236.26	11.609%	$263.6874	$263.69	$263.70	$263.70
7 purchase totals =	$1,337.54		$1,459.5903	$1,459.59	$1,459.60	$1,459.70