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	$30.42	10.729%	$33.6838	$33.68	$33.70	$33.70
Purchase #2	$151.35	12.697%	$170.5669	$170.57	$170.55	$170.60
Purchase #3	$25.79	8.126%	$27.8857	$27.89	$27.90	$27.90
Purchase #4	$176.42	11.262%	$196.2884	$196.29	$196.30	$196.30
Purchase #5	$48.77	5.723%	$51.5611	$51.56	$51.55	$51.60
Purchase #6	$6.27	4.337%	$6.5419	$6.54	$6.55	$6.50
Purchase #7	$157.45	8.154%	$170.2885	$170.29	$170.30	$170.30
7 purchase totals =	$596.47		$656.8163	$656.82	$656.85	$656.90