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	$90.72	10.314%	$100.0769	$100.08	$100.10	$100.10
Purchase #2	$16.69	8.598%	$18.125	$18.13	$18.15	$18.10
Purchase #3	$225.38	4.171%	$234.7806	$234.78	$234.80	$234.80
Purchase #4	$80.68	7.361%	$86.6189	$86.62	$86.60	$86.60
Purchase #5	$137.26	13.111%	$155.2562	$155.26	$155.25	$155.30
Purchase #6	$182.37	3.220%	$188.2423	$188.24	$188.25	$188.20
Purchase #7	$41.28	9.238%	$45.0934	$45.09	$45.10	$45.10
7 purchase totals =	$774.38		$828.1933	$828.20	$828.25	$828.20