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	$136.42	3.420%	$141.0856	$141.09	$141.10	$141.10
Purchase #2	$93.52	7.228%	$100.2796	$100.28	$100.30	$100.30
Purchase #3	$49.28	7.288%	$52.8715	$52.87	$52.85	$52.90
Purchase #4	$174.45	8.836%	$189.8644	$189.86	$189.85	$189.90
Purchase #5	$62.25	5.139%	$65.449	$65.45	$65.45	$65.40
Purchase #6	$225.29	10.575%	$249.1144	$249.11	$249.10	$249.10
Purchase #7	$93.40	9.239%	$102.0292	$102.03	$102.05	$102.00
7 purchase totals =	$834.61		$900.6937	$900.69	$900.70	$900.70