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	$18.68	10.570%	$20.6545	$20.65	$20.65	$20.70
Purchase #2	$78.76	3.533%	$81.5426	$81.54	$81.55	$81.50
Purchase #3	$32.45	4.348%	$33.8609	$33.86	$33.85	$33.90
Purchase #4	$48.38	13.223%	$54.7773	$54.78	$54.80	$54.80
Purchase #5	$223.35	12.191%	$250.5786	$250.58	$250.60	$250.60
Purchase #6	$6.76	3.846%	$7.02	$7.02	$7.00	$7.00
Purchase #7	$216.82	5.225%	$228.1488	$228.15	$228.15	$228.10
7 purchase totals =	$625.20		$676.5827	$676.58	$676.60	$676.60