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	$22.48	12.247%	$25.2331	$25.23	$25.25	$25.20
Purchase #2	$80.60	10.867%	$89.3588	$89.36	$89.35	$89.40
Purchase #3	$34.33	5.159%	$36.1011	$36.10	$36.10	$36.10
Purchase #4	$10.85	4.698%	$11.3597	$11.36	$11.35	$11.40
Purchase #5	$162.91	13.768%	$185.3394	$185.34	$185.35	$185.30
Purchase #6	$60.90	8.229%	$65.9115	$65.91	$65.90	$65.90
Purchase #7	$225.97	13.147%	$255.6783	$255.68	$255.70	$255.70
7 purchase totals =	$598.04		$668.9819	$668.98	$669.00	$669.00