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	$77.44	6.468%	$82.4488	$82.45	$82.45	$82.40
Purchase #2	$122.81	12.610%	$138.2963	$138.30	$138.30	$138.30
Purchase #3	$100.95	4.865%	$105.8612	$105.86	$105.85	$105.90
Purchase #4	$172.27	7.868%	$185.8242	$185.82	$185.80	$185.80
Purchase #5	$236.47	8.519%	$256.6149	$256.61	$256.60	$256.60
Purchase #6	$41.95	7.805%	$45.2242	$45.22	$45.20	$45.20
Purchase #7	$75.83	4.694%	$79.3895	$79.39	$79.40	$79.40
7 purchase totals =	$827.72		$893.6591	$893.65	$893.60	$893.60