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	$210.29	11.651%	$234.7909	$234.79	$234.80	$234.80
Purchase #2	$94.60	11.257%	$105.2491	$105.25	$105.25	$105.20
Purchase #3	$108.30	10.249%	$119.3997	$119.40	$119.40	$119.40
Purchase #4	$35.36	9.288%	$38.6442	$38.64	$38.65	$38.60
Purchase #5	$108.50	3.382%	$112.1695	$112.17	$112.15	$112.20
Purchase #6	$55.27	13.215%	$62.5739	$62.57	$62.55	$62.60
Purchase #7	$91.29	10.505%	$100.88	$100.88	$100.90	$100.90
7 purchase totals =	$703.61		$773.7073	$773.70	$773.70	$773.70