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	$178.65	13.800%	$203.3037	$203.30	$203.30	$203.30
Purchase #2	$111.87	13.543%	$127.0206	$127.02	$127.00	$127.00
Purchase #3	$12.39	13.631%	$14.0789	$14.08	$14.10	$14.10
Purchase #4	$102.99	8.322%	$111.5608	$111.56	$111.55	$111.60
Purchase #5	$38.41	12.673%	$43.2777	$43.28	$43.30	$43.30
Purchase #6	$80.40	3.790%	$83.4472	$83.45	$83.45	$83.40
Purchase #7	$13.69	12.314%	$15.3758	$15.38	$15.40	$15.40
7 purchase totals =	$538.40		$598.0647	$598.07	$598.10	$598.10