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	$155.48	12.500%	$174.915	$174.92	$174.90	$174.90
Purchase #2	$158.45	13.269%	$179.4747	$179.47	$179.45	$179.50
Purchase #3	$66.51	5.517%	$70.1794	$70.18	$70.20	$70.20
Purchase #4	$216.37	12.852%	$244.1779	$244.18	$244.20	$244.20
Purchase #5	$67.45	6.627%	$71.9199	$71.92	$71.90	$71.90
Purchase #6	$43.87	10.802%	$48.6088	$48.61	$48.60	$48.60
Purchase #7	$177.73	6.320%	$188.9625	$188.96	$188.95	$189.00
7 purchase totals =	$885.86		$978.2382	$978.24	$978.20	$978.30