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	$82.75	9.654%	$90.7387	$90.74	$90.75	$90.70
Purchase #2	$249.65	5.482%	$263.3358	$263.34	$263.35	$263.30
Purchase #3	$158.32	13.660%	$179.9465	$179.95	$179.95	$179.90
Purchase #4	$136.34	13.806%	$155.1631	$155.16	$155.15	$155.20
Purchase #5	$19.86	8.270%	$21.5024	$21.50	$21.50	$21.50
Purchase #6	$76.82	13.855%	$87.4634	$87.46	$87.45	$87.50
Purchase #7	$52.51	9.341%	$57.415	$57.42	$57.40	$57.40
7 purchase totals =	$776.25		$855.5649	$855.57	$855.55	$855.50