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	$102.35	6.356%	$108.8554	$108.86	$108.85	$108.90
Purchase #2	$76.62	5.421%	$80.7736	$80.77	$80.75	$80.80
Purchase #3	$32.46	8.454%	$35.2042	$35.20	$35.20	$35.20
Purchase #4	$117.89	5.140%	$123.9495	$123.95	$123.95	$123.90
Purchase #5	$206.98	3.708%	$214.6548	$214.65	$214.65	$214.70
Purchase #6	$116.27	5.874%	$123.0997	$123.10	$123.10	$123.10
Purchase #7	$138.61	10.332%	$152.9312	$152.93	$152.95	$152.90
7 purchase totals =	$791.18		$839.4684	$839.46	$839.45	$839.50