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	$63.88	10.335%	$70.482	$70.48	$70.50	$70.50
Purchase #2	$63.47	3.642%	$65.7816	$65.78	$65.80	$65.80
Purchase #3	$85.42	6.874%	$91.2918	$91.29	$91.30	$91.30
Purchase #4	$14.59	5.194%	$15.3478	$15.35	$15.35	$15.30
Purchase #5	$94.47	11.630%	$105.4569	$105.46	$105.45	$105.50
Purchase #6	$62.54	13.874%	$71.2168	$71.22	$71.20	$71.20
Purchase #7	$100.30	3.425%	$103.7353	$103.74	$103.75	$103.70
7 purchase totals =	$484.67		$523.3122	$523.32	$523.35	$523.30