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	$167.47	10.621%	$185.257	$185.26	$185.25	$185.30
Purchase #2	$93.78	9.777%	$102.9489	$102.95	$102.95	$102.90
Purchase #3	$17.64	5.581%	$18.6245	$18.62	$18.60	$18.60
Purchase #4	$56.73	5.104%	$59.6255	$59.63	$59.65	$59.60
Purchase #5	$69.97	6.264%	$74.3529	$74.35	$74.35	$74.40
Purchase #6	$35.27	3.530%	$36.515	$36.52	$36.50	$36.50
Purchase #7	$137.88	4.448%	$144.0129	$144.01	$144.00	$144.00
7 purchase totals =	$578.74		$621.3367	$621.34	$621.30	$621.30