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	$248.83	8.823%	$270.7843	$270.78	$270.80	$270.80
Purchase #2	$89.91	3.281%	$92.8599	$92.86	$92.85	$92.90
Purchase #3	$7.66	10.150%	$8.4375	$8.44	$8.45	$8.40
Purchase #4	$138.81	10.414%	$153.2657	$153.27	$153.25	$153.30
Purchase #5	$37.89	5.571%	$40.0009	$40.00	$40.00	$40.00
Purchase #6	$43.95	4.531%	$45.9414	$45.94	$45.95	$45.90
Purchase #7	$108.62	13.775%	$123.5824	$123.58	$123.60	$123.60
7 purchase totals =	$675.67		$734.8721	$734.87	$734.90	$734.90