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	$29.85	13.523%	$33.8866	$33.89	$33.90	$33.90
Purchase #2	$147.91	13.208%	$167.446	$167.45	$167.45	$167.40
Purchase #3	$153.35	8.559%	$166.4752	$166.48	$166.50	$166.50
Purchase #4	$124.52	5.831%	$131.7808	$131.78	$131.80	$131.80
Purchase #5	$203.81	9.762%	$223.7059	$223.71	$223.70	$223.70
Purchase #6	$90.85	13.307%	$102.9394	$102.94	$102.95	$102.90
Purchase #7	$88.78	8.717%	$96.519	$96.52	$96.50	$96.50
7 purchase totals =	$839.07		$922.7529	$922.77	$922.80	$922.70