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	$249.47	13.384%	$282.8591	$282.86	$282.85	$282.90
Purchase #2	$81.64	11.675%	$91.1715	$91.17	$91.15	$91.20
Purchase #3	$198.26	13.795%	$225.61	$225.61	$225.60	$225.60
Purchase #4	$101.97	10.253%	$112.425	$112.43	$112.45	$112.40
Purchase #5	$79.54	5.219%	$83.6912	$83.69	$83.70	$83.70
Purchase #6	$9.27	12.471%	$10.4261	$10.43	$10.45	$10.40
Purchase #7	$40.25	12.668%	$45.3489	$45.35	$45.35	$45.30
7 purchase totals =	$760.40		$851.5318	$851.54	$851.55	$851.50