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	$140.87	7.297%	$151.1493	$151.15	$151.15	$151.10
Purchase #2	$22.80	8.268%	$24.6851	$24.69	$24.70	$24.70
Purchase #3	$154.31	8.110%	$166.8245	$166.82	$166.80	$166.80
Purchase #4	$165.70	11.736%	$185.1466	$185.15	$185.15	$185.10
Purchase #5	$177.57	10.531%	$196.2699	$196.27	$196.25	$196.30
Purchase #6	$35.41	9.569%	$38.7984	$38.80	$38.80	$38.80
Purchase #7	$63.75	3.594%	$66.0412	$66.04	$66.05	$66.00
7 purchase totals =	$760.41		$828.9150	$828.92	$828.90	$828.80