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	$15.86	9.125%	$17.3072	$17.31	$17.30	$17.30
Purchase #2	$83.33	7.781%	$89.8139	$89.81	$89.80	$89.80
Purchase #3	$49.63	13.236%	$56.199	$56.20	$56.20	$56.20
Purchase #4	$13.97	11.771%	$15.6144	$15.61	$15.60	$15.60
Purchase #5	$49.35	5.628%	$52.1274	$52.13	$52.15	$52.10
Purchase #6	$61.92	5.238%	$65.1634	$65.16	$65.15	$65.20
Purchase #7	$219.95	8.355%	$238.3268	$238.33	$238.35	$238.30
7 purchase totals =	$494.01		$534.5521	$534.55	$534.55	$534.50