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	$90.87	10.586%	$100.4895	$100.49	$100.50	$100.50
Purchase #2	$200.87	8.410%	$217.7632	$217.76	$217.75	$217.80
Purchase #3	$105.63	9.450%	$115.612	$115.61	$115.60	$115.60
Purchase #4	$24.27	4.786%	$25.4316	$25.43	$25.45	$25.40
Purchase #5	$244.81	10.659%	$270.9043	$270.90	$270.90	$270.90
Purchase #6	$66.41	7.416%	$71.335	$71.34	$71.35	$71.30
Purchase #7	$49.78	4.105%	$51.8235	$51.82	$51.80	$51.80
7 purchase totals =	$782.64		$853.3591	$853.35	$853.35	$853.30