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	$49.76	8.296%	$53.8881	$53.89	$53.90	$53.90
Purchase #2	$27.38	7.353%	$29.3933	$29.39	$29.40	$29.40
Purchase #3	$133.34	4.784%	$139.719	$139.72	$139.70	$139.70
Purchase #4	$91.44	8.244%	$98.9783	$98.98	$99.00	$99.00
Purchase #5	$114.32	9.126%	$124.7528	$124.75	$124.75	$124.80
Purchase #6	$29.85	12.569%	$33.6018	$33.60	$33.60	$33.60
Purchase #7	$214.29	8.111%	$231.6711	$231.67	$231.65	$231.70
7 purchase totals =	$660.38		$712.0044	$712.00	$712.00	$712.10