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	$69.99	3.645%	$72.5411	$72.54	$72.55	$72.50
Purchase #2	$75.28	4.501%	$78.6684	$78.67	$78.65	$78.70
Purchase #3	$83.49	10.577%	$92.3207	$92.32	$92.30	$92.30
Purchase #4	$118.32	6.278%	$125.7481	$125.75	$125.75	$125.70
Purchase #5	$152.82	13.283%	$173.1191	$173.12	$173.10	$173.10
Purchase #6	$82.32	10.304%	$90.8023	$90.80	$90.80	$90.80
Purchase #7	$9.65	3.630%	$10.0003	$10.00	$10.00	$10.00
7 purchase totals =	$591.87		$643.2000	$643.20	$643.15	$643.10