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	$51.64	10.413%	$57.0173	$57.02	$57.00	$57.00
Purchase #2	$97.69	13.866%	$111.2357	$111.24	$111.25	$111.20
Purchase #3	$91.32	10.389%	$100.8072	$100.81	$100.80	$100.80
Purchase #4	$80.28	6.643%	$85.613	$85.61	$85.60	$85.60
Purchase #5	$67.78	3.194%	$69.9449	$69.94	$69.95	$69.90
Purchase #6	$45.35	8.441%	$49.178	$49.18	$49.20	$49.20
Purchase #7	$36.40	5.242%	$38.3081	$38.31	$38.30	$38.30
7 purchase totals =	$470.46		$512.1042	$512.11	$512.10	$512.00