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	$101.93	13.426%	$115.6151	$115.62	$115.60	$115.60
Purchase #2	$81.52	11.466%	$90.8671	$90.87	$90.85	$90.90
Purchase #3	$58.31	5.404%	$61.4611	$61.46	$61.45	$61.50
Purchase #4	$162.29	6.362%	$172.6149	$172.61	$172.60	$172.60
Purchase #5	$178.97	4.352%	$186.7588	$186.76	$186.75	$186.80
Purchase #6	$171.36	7.429%	$184.0903	$184.09	$184.10	$184.10
Purchase #7	$10.45	5.470%	$11.0216	$11.02	$11.00	$11.00
7 purchase totals =	$764.83		$822.4289	$822.43	$822.35	$822.50