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	$145.93	11.628%	$162.8987	$162.90	$162.90	$162.90
Purchase #2	$232.41	13.517%	$263.8249	$263.82	$263.80	$263.80
Purchase #3	$172.84	9.232%	$188.7966	$188.80	$188.80	$188.80
Purchase #4	$83.54	7.543%	$89.8414	$89.84	$89.85	$89.80
Purchase #5	$128.38	4.133%	$133.6859	$133.69	$133.70	$133.70
Purchase #6	$32.27	6.133%	$34.2491	$34.25	$34.25	$34.20
Purchase #7	$100.55	10.695%	$111.3038	$111.30	$111.30	$111.30
7 purchase totals =	$895.92		$984.6004	$984.60	$984.60	$984.50