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	$90.34	10.718%	$100.0226	$100.02	$100.00	$100.00
Purchase #2	$47.54	10.402%	$52.4851	$52.49	$52.50	$52.50
Purchase #3	$163.58	4.215%	$170.4749	$170.47	$170.45	$170.50
Purchase #4	$68.88	5.120%	$72.4067	$72.41	$72.40	$72.40
Purchase #5	$83.61	3.215%	$86.2981	$86.30	$86.30	$86.30
Purchase #6	$60.85	7.609%	$65.4801	$65.48	$65.50	$65.50
Purchase #7	$124.55	10.638%	$137.7996	$137.80	$137.80	$137.80
7 purchase totals =	$639.35		$684.9671	$684.97	$684.95	$685.00