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	$44.83	11.363%	$49.924	$49.92	$49.90	$49.90
Purchase #2	$198.62	6.447%	$211.425	$211.43	$211.45	$211.40
Purchase #3	$194.89	4.663%	$203.9777	$203.98	$204.00	$204.00
Purchase #4	$158.85	4.432%	$165.8902	$165.89	$165.90	$165.90
Purchase #5	$119.82	6.491%	$127.5975	$127.60	$127.60	$127.60
Purchase #6	$7.79	8.740%	$8.4708	$8.47	$8.45	$8.50
Purchase #7	$145.39	8.736%	$158.0913	$158.09	$158.10	$158.10
7 purchase totals =	$870.19		$925.3765	$925.38	$925.40	$925.40