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	$24.50	12.127%	$27.4711	$27.47	$27.45	$27.50
Purchase #2	$13.39	13.673%	$15.2208	$15.22	$15.20	$15.20
Purchase #3	$88.59	7.825%	$95.5222	$95.52	$95.50	$95.50
Purchase #4	$9.39	12.453%	$10.5593	$10.56	$10.55	$10.60
Purchase #5	$31.68	13.244%	$35.8757	$35.88	$35.90	$35.90
Purchase #6	$91.60	10.379%	$101.1072	$101.11	$101.10	$101.10
Purchase #7	$80.34	12.128%	$90.0836	$90.08	$90.10	$90.10
7 purchase totals =	$339.49		$375.8399	$375.84	$375.80	$375.90