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	$109.40	11.104%	$121.5478	$121.55	$121.55	$121.50
Purchase #2	$212.48	12.280%	$238.5725	$238.57	$238.55	$238.60
Purchase #3	$37.27	8.505%	$40.4398	$40.44	$40.45	$40.40
Purchase #4	$219.43	13.622%	$249.3208	$249.32	$249.30	$249.30
Purchase #5	$136.54	4.501%	$142.6857	$142.69	$142.70	$142.70
Purchase #6	$187.93	10.746%	$208.125	$208.13	$208.15	$208.10
Purchase #7	$99.61	9.244%	$108.8179	$108.82	$108.80	$108.80
7 purchase totals =	$1,002.66		$1,109.5095	$1,109.52	$1,109.50	$1,109.40