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	$241.82	13.791%	$275.1694	$275.17	$275.15	$275.20
Purchase #2	$228.87	11.825%	$255.9339	$255.93	$255.95	$255.90
Purchase #3	$15.67	3.836%	$16.2711	$16.27	$16.25	$16.30
Purchase #4	$97.29	8.482%	$105.5421	$105.54	$105.55	$105.50
Purchase #5	$65.27	10.831%	$72.3394	$72.34	$72.35	$72.30
Purchase #6	$99.91	3.579%	$103.4858	$103.49	$103.50	$103.50
Purchase #7	$141.55	10.324%	$156.1636	$156.16	$156.15	$156.20
7 purchase totals =	$890.38		$984.9053	$984.90	$984.90	$984.90