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	$67.47	7.417%	$72.4742	$72.47	$72.45	$72.50
Purchase #2	$53.93	4.502%	$56.3579	$56.36	$56.35	$56.40
Purchase #3	$185.72	10.786%	$205.7518	$205.75	$205.75	$205.80
Purchase #4	$46.85	12.293%	$52.6093	$52.61	$52.60	$52.60
Purchase #5	$199.57	7.293%	$214.1246	$214.12	$214.10	$214.10
Purchase #6	$136.99	10.836%	$151.8342	$151.83	$151.85	$151.80
Purchase #7	$73.30	12.423%	$82.4061	$82.41	$82.40	$82.40
7 purchase totals =	$763.83		$835.5581	$835.55	$835.50	$835.60