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	$132.95	8.747%	$144.5791	$144.58	$144.60	$144.60
Purchase #2	$228.38	5.389%	$240.6874	$240.69	$240.70	$240.70
Purchase #3	$61.74	6.214%	$65.5765	$65.58	$65.60	$65.60
Purchase #4	$37.63	12.265%	$42.2453	$42.25	$42.25	$42.20
Purchase #5	$241.64	13.340%	$273.8748	$273.87	$273.85	$273.90
Purchase #6	$10.32	9.648%	$11.3157	$11.32	$11.30	$11.30
Purchase #7	$104.54	13.664%	$118.8243	$118.82	$118.80	$118.80
7 purchase totals =	$817.20		$897.1031	$897.11	$897.10	$897.10