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	$45.47	12.641%	$51.2179	$51.22	$51.20	$51.20
Purchase #2	$14.83	6.504%	$15.7945	$15.79	$15.80	$15.80
Purchase #3	$35.37	6.545%	$37.685	$37.69	$37.70	$37.70
Purchase #4	$174.39	8.839%	$189.8043	$189.80	$189.80	$189.80
Purchase #5	$242.90	5.190%	$255.5065	$255.51	$255.50	$255.50
Purchase #6	$124.60	11.219%	$138.5789	$138.58	$138.60	$138.60
Purchase #7	$29.66	11.827%	$33.1679	$33.17	$33.15	$33.20
7 purchase totals =	$667.22		$721.7550	$721.76	$721.75	$721.80