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	$138.41	5.661%	$146.2454	$146.25	$146.25	$146.20
Purchase #2	$164.51	10.808%	$182.2902	$182.29	$182.30	$182.30
Purchase #3	$230.59	8.554%	$250.3147	$250.31	$250.30	$250.30
Purchase #4	$139.82	3.750%	$145.0633	$145.06	$145.05	$145.10
Purchase #5	$183.37	12.635%	$206.5388	$206.54	$206.55	$206.50
Purchase #6	$106.25	13.776%	$120.887	$120.89	$120.90	$120.90
Purchase #7	$91.52	9.857%	$100.5411	$100.54	$100.55	$100.50
7 purchase totals =	$1,054.47		$1,151.8805	$1,151.88	$1,151.90	$1,151.80