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	$57.27	10.130%	$63.0715	$63.07	$63.05	$63.10
Purchase #2	$57.82	6.578%	$61.6234	$61.62	$61.60	$61.60
Purchase #3	$197.77	8.871%	$215.3142	$215.31	$215.30	$215.30
Purchase #4	$132.25	10.183%	$145.717	$145.72	$145.70	$145.70
Purchase #5	$145.58	7.544%	$156.5626	$156.56	$156.55	$156.60
Purchase #6	$35.60	13.621%	$40.4491	$40.45	$40.45	$40.40
Purchase #7	$80.39	13.253%	$91.0441	$91.04	$91.05	$91.00
7 purchase totals =	$706.68		$773.7819	$773.77	$773.70	$773.70