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	$151.87	12.680%	$171.1271	$171.13	$171.15	$171.10
Purchase #2	$108.46	7.223%	$116.2941	$116.29	$116.30	$116.30
Purchase #3	$32.91	4.326%	$34.3337	$34.33	$34.35	$34.30
Purchase #4	$33.80	13.861%	$38.485	$38.49	$38.50	$38.50
Purchase #5	$60.88	11.401%	$67.8209	$67.82	$67.80	$67.80
Purchase #6	$166.54	12.284%	$186.9978	$187.00	$187.00	$187.00
Purchase #7	$142.59	7.857%	$153.7933	$153.79	$153.80	$153.80
7 purchase totals =	$697.05		$768.8519	$768.85	$768.90	$768.80