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	$123.43	3.626%	$127.9056	$127.91	$127.90	$127.90
Purchase #2	$149.48	3.665%	$154.9584	$154.96	$154.95	$155.00
Purchase #3	$103.85	7.743%	$111.8911	$111.89	$111.90	$111.90
Purchase #4	$42.54	13.547%	$48.3029	$48.30	$48.30	$48.30
Purchase #5	$28.61	4.454%	$29.8843	$29.88	$29.90	$29.90
Purchase #6	$142.89	6.209%	$151.762	$151.76	$151.75	$151.80
Purchase #7	$112.78	7.461%	$121.1945	$121.19	$121.20	$121.20
7 purchase totals =	$703.58		$745.8988	$745.89	$745.90	$746.00