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	$227.80	5.314%	$239.9053	$239.91	$239.90	$239.90
Purchase #2	$89.95	13.228%	$101.8486	$101.85	$101.85	$101.80
Purchase #3	$77.49	12.691%	$87.3243	$87.32	$87.30	$87.30
Purchase #4	$18.72	9.652%	$20.5269	$20.53	$20.55	$20.50
Purchase #5	$46.29	9.853%	$50.851	$50.85	$50.85	$50.90
Purchase #6	$245.90	8.233%	$266.1449	$266.14	$266.15	$266.10
Purchase #7	$233.83	12.837%	$263.8468	$263.85	$263.85	$263.80
7 purchase totals =	$939.98		$1,030.4478	$1,030.45	$1,030.45	$1,030.30