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	$16.25	11.587%	$18.1329	$18.13	$18.15	$18.10
Purchase #2	$34.56	3.837%	$35.8861	$35.89	$35.90	$35.90
Purchase #3	$223.47	12.580%	$251.5825	$251.58	$251.60	$251.60
Purchase #4	$41.38	4.167%	$43.1043	$43.10	$43.10	$43.10
Purchase #5	$194.68	12.631%	$219.27	$219.27	$219.25	$219.30
Purchase #6	$121.50	6.809%	$129.7729	$129.77	$129.75	$129.80
Purchase #7	$60.77	11.652%	$67.8509	$67.85	$67.85	$67.90
7 purchase totals =	$692.61		$765.5996	$765.59	$765.60	$765.70