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	$102.62	8.786%	$111.6362	$111.64	$111.65	$111.60
Purchase #2	$244.27	4.726%	$255.8142	$255.81	$255.80	$255.80
Purchase #3	$109.91	12.630%	$123.7916	$123.79	$123.80	$123.80
Purchase #4	$81.82	4.714%	$85.677	$85.68	$85.70	$85.70
Purchase #5	$160.68	13.228%	$181.9348	$181.93	$181.95	$181.90
Purchase #6	$24.82	9.860%	$27.2673	$27.27	$27.25	$27.30
Purchase #7	$45.30	8.398%	$49.1043	$49.10	$49.10	$49.10
7 purchase totals =	$769.42		$835.2254	$835.22	$835.25	$835.20