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	$239.94	12.254%	$269.3422	$269.34	$269.35	$269.30
Purchase #2	$45.82	4.381%	$47.8274	$47.83	$47.85	$47.80
Purchase #3	$112.81	5.766%	$119.3146	$119.31	$119.30	$119.30
Purchase #4	$6.81	8.851%	$7.4128	$7.41	$7.40	$7.40
Purchase #5	$97.69	5.710%	$103.2681	$103.27	$103.25	$103.30
Purchase #6	$223.60	8.247%	$242.0403	$242.04	$242.05	$242.00
Purchase #7	$33.99	10.371%	$37.5151	$37.52	$37.50	$37.50
7 purchase totals =	$760.66		$826.7205	$826.72	$826.70	$826.60