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	$79.83	12.661%	$89.9373	$89.94	$89.95	$89.90
Purchase #2	$111.98	5.873%	$118.5566	$118.56	$118.55	$118.60
Purchase #3	$126.29	12.665%	$142.2846	$142.28	$142.30	$142.30
Purchase #4	$196.69	13.873%	$223.9768	$223.98	$224.00	$224.00
Purchase #5	$11.82	3.608%	$12.2465	$12.25	$12.25	$12.20
Purchase #6	$21.85	10.195%	$24.0776	$24.08	$24.10	$24.10
Purchase #7	$200.97	6.102%	$213.2332	$213.23	$213.25	$213.20
7 purchase totals =	$749.43		$824.3126	$824.32	$824.40	$824.30