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	$81.82	10.759%	$90.623	$90.62	$90.60	$90.60
Purchase #2	$61.41	7.144%	$65.7971	$65.80	$65.80	$65.80
Purchase #3	$233.60	12.658%	$263.1691	$263.17	$263.15	$263.20
Purchase #4	$100.84	11.487%	$112.4235	$112.42	$112.40	$112.40
Purchase #5	$33.46	12.645%	$37.691	$37.69	$37.70	$37.70
Purchase #6	$126.78	12.332%	$142.4145	$142.41	$142.40	$142.40
Purchase #7	$127.47	8.334%	$138.0933	$138.09	$138.10	$138.10
7 purchase totals =	$765.38		$850.2115	$850.20	$850.15	$850.20