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	$81.60	11.444%	$90.9383	$90.94	$90.95	$90.90
Purchase #2	$9.47	11.869%	$10.594	$10.59	$10.60	$10.60
Purchase #3	$68.64	8.315%	$74.3474	$74.35	$74.35	$74.30
Purchase #4	$83.33	7.840%	$89.8631	$89.86	$89.85	$89.90
Purchase #5	$220.46	7.687%	$237.4068	$237.41	$237.40	$237.40
Purchase #6	$29.85	8.663%	$32.4359	$32.44	$32.45	$32.40
Purchase #7	$75.49	9.691%	$82.8057	$82.81	$82.80	$82.80
7 purchase totals =	$568.84		$618.3912	$618.40	$618.40	$618.30