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	$105.45	3.209%	$108.8339	$108.83	$108.85	$108.80
Purchase #2	$140.84	9.185%	$153.7762	$153.78	$153.80	$153.80
Purchase #3	$84.78	8.805%	$92.2449	$92.24	$92.25	$92.20
Purchase #4	$238.28	7.481%	$256.1057	$256.11	$256.10	$256.10
Purchase #5	$45.56	13.164%	$51.5575	$51.56	$51.55	$51.60
Purchase #6	$82.84	3.641%	$85.8562	$85.86	$85.85	$85.90
Purchase #7	$128.48	6.525%	$136.8633	$136.86	$136.85	$136.90
7 purchase totals =	$826.23		$885.2377	$885.24	$885.25	$885.30