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	$54.83	10.269%	$60.4605	$60.46	$60.45	$60.50
Purchase #2	$194.77	9.704%	$213.6705	$213.67	$213.65	$213.70
Purchase #3	$45.37	8.762%	$49.3453	$49.35	$49.35	$49.30
Purchase #4	$42.61	10.869%	$47.2413	$47.24	$47.25	$47.20
Purchase #5	$78.99	13.813%	$89.9009	$89.90	$89.90	$89.90
Purchase #6	$48.49	9.429%	$53.0621	$53.06	$53.05	$53.10
Purchase #7	$138.69	10.816%	$153.6907	$153.69	$153.70	$153.70
7 purchase totals =	$603.75		$667.3713	$667.37	$667.35	$667.40