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	$100.59	11.247%	$111.9034	$111.90	$111.90	$111.90
Purchase #2	$182.82	3.500%	$189.2187	$189.22	$189.20	$189.20
Purchase #3	$245.99	10.822%	$272.611	$272.61	$272.60	$272.60
Purchase #4	$60.90	3.401%	$62.9712	$62.97	$62.95	$63.00
Purchase #5	$28.75	9.112%	$31.3697	$31.37	$31.35	$31.40
Purchase #6	$114.69	10.678%	$126.9366	$126.94	$126.95	$126.90
Purchase #7	$65.42	3.711%	$67.8477	$67.85	$67.85	$67.80
7 purchase totals =	$799.16		$862.8583	$862.86	$862.80	$862.80