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	$59.91	11.779%	$66.9668	$66.97	$66.95	$67.00
Purchase #2	$71.87	9.792%	$78.9075	$78.91	$78.90	$78.90
Purchase #3	$244.77	13.752%	$278.4308	$278.43	$278.45	$278.40
Purchase #4	$145.37	3.308%	$150.1788	$150.18	$150.20	$150.20
Purchase #5	$116.41	6.767%	$124.2875	$124.29	$124.30	$124.30
Purchase #6	$67.68	13.246%	$76.6449	$76.64	$76.65	$76.60
Purchase #7	$51.54	12.426%	$57.9444	$57.94	$57.95	$57.90
7 purchase totals =	$757.55		$833.3607	$833.36	$833.40	$833.30