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	$165.78	4.534%	$173.2965	$173.30	$173.30	$173.30
Purchase #2	$80.33	12.278%	$90.1929	$90.19	$90.20	$90.20
Purchase #3	$153.92	9.718%	$168.8779	$168.88	$168.90	$168.90
Purchase #4	$69.94	4.336%	$72.9726	$72.97	$72.95	$73.00
Purchase #5	$44.62	8.221%	$48.2882	$48.29	$48.30	$48.30
Purchase #6	$156.86	10.785%	$173.7774	$173.78	$173.80	$173.80
Purchase #7	$92.79	13.548%	$105.3612	$105.36	$105.35	$105.40
7 purchase totals =	$764.24		$832.7667	$832.77	$832.80	$832.90