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	$7.65	7.546%	$8.2273	$8.23	$8.25	$8.20
Purchase #2	$16.60	9.344%	$18.1511	$18.15	$18.15	$18.20
Purchase #3	$88.56	13.600%	$100.6042	$100.60	$100.60	$100.60
Purchase #4	$58.98	11.708%	$65.8854	$65.89	$65.90	$65.90
Purchase #5	$127.88	12.664%	$144.0747	$144.07	$144.05	$144.10
Purchase #6	$162.48	5.144%	$170.838	$170.84	$170.85	$170.80
Purchase #7	$105.54	3.545%	$109.2814	$109.28	$109.30	$109.30
7 purchase totals =	$567.69		$617.0621	$617.06	$617.10	$617.10