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	$58.83	12.747%	$66.3291	$66.33	$66.35	$66.30
Purchase #2	$81.29	9.588%	$89.0841	$89.08	$89.10	$89.10
Purchase #3	$151.25	11.111%	$168.0554	$168.06	$168.05	$168.10
Purchase #4	$62.96	13.521%	$71.4728	$71.47	$71.45	$71.50
Purchase #5	$162.95	10.727%	$180.4296	$180.43	$180.45	$180.40
Purchase #6	$93.57	7.423%	$100.5157	$100.52	$100.50	$100.50
Purchase #7	$49.92	5.556%	$52.6936	$52.69	$52.70	$52.70
7 purchase totals =	$660.77		$728.5803	$728.58	$728.60	$728.60