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	$127.60	7.552%	$137.2364	$137.24	$137.25	$137.20
Purchase #2	$148.57	5.520%	$156.7711	$156.77	$156.75	$156.80
Purchase #3	$15.87	10.591%	$17.5508	$17.55	$17.55	$17.60
Purchase #4	$14.60	4.357%	$15.2361	$15.24	$15.25	$15.20
Purchase #5	$52.74	12.457%	$59.3098	$59.31	$59.30	$59.30
Purchase #6	$102.73	11.516%	$114.5604	$114.56	$114.55	$114.60
Purchase #7	$34.35	11.314%	$38.2364	$38.24	$38.25	$38.20
7 purchase totals =	$496.46		$538.9010	$538.91	$538.90	$538.90