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	$186.86	6.461%	$198.933	$198.93	$198.95	$198.90
Purchase #2	$149.75	10.837%	$165.9784	$165.98	$166.00	$166.00
Purchase #3	$50.47	13.799%	$57.4344	$57.43	$57.45	$57.40
Purchase #4	$167.62	9.270%	$183.1584	$183.16	$183.15	$183.20
Purchase #5	$40.90	11.500%	$45.6035	$45.60	$45.60	$45.60
Purchase #6	$104.65	7.500%	$112.4988	$112.50	$112.50	$112.50
Purchase #7	$26.89	11.363%	$29.9455	$29.95	$29.95	$29.90
7 purchase totals =	$727.14		$793.5520	$793.55	$793.60	$793.50