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	$79.60	8.668%	$86.4997	$86.50	$86.50	$86.50
Purchase #2	$102.78	6.872%	$109.843	$109.84	$109.85	$109.80
Purchase #3	$44.63	10.822%	$49.4599	$49.46	$49.45	$49.50
Purchase #4	$82.35	11.531%	$91.8458	$91.85	$91.85	$91.80
Purchase #5	$176.85	7.720%	$190.5028	$190.50	$190.50	$190.50
Purchase #6	$184.90	7.806%	$199.3333	$199.33	$199.35	$199.30
Purchase #7	$49.36	4.810%	$51.7342	$51.73	$51.75	$51.70
7 purchase totals =	$720.47		$779.2187	$779.21	$779.25	$779.10