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	$53.89	10.452%	$59.5226	$59.52	$59.50	$59.50
Purchase #2	$73.84	13.642%	$83.9133	$83.91	$83.90	$83.90
Purchase #3	$205.93	9.690%	$225.8846	$225.88	$225.90	$225.90
Purchase #4	$17.61	6.280%	$18.7159	$18.72	$18.70	$18.70
Purchase #5	$16.37	8.719%	$17.7973	$17.80	$17.80	$17.80
Purchase #6	$76.69	8.363%	$83.1036	$83.10	$83.10	$83.10
Purchase #7	$75.28	11.194%	$83.7068	$83.71	$83.70	$83.70
7 purchase totals =	$519.61		$572.6441	$572.64	$572.60	$572.60