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	$192.77	9.122%	$210.3545	$210.35	$210.35	$210.40
Purchase #2	$132.50	7.255%	$142.1129	$142.11	$142.10	$142.10
Purchase #3	$246.93	10.467%	$272.7762	$272.78	$272.80	$272.80
Purchase #4	$39.52	7.355%	$42.4267	$42.43	$42.45	$42.40
Purchase #5	$49.37	11.689%	$55.1409	$55.14	$55.15	$55.10
Purchase #6	$161.55	3.744%	$167.5984	$167.60	$167.60	$167.60
Purchase #7	$41.45	12.156%	$46.4887	$46.49	$46.50	$46.50
7 purchase totals =	$864.09		$936.8983	$936.90	$936.95	$936.90