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	$27.72	6.852%	$29.6194	$29.62	$29.60	$29.60
Purchase #2	$168.93	11.372%	$188.1407	$188.14	$188.15	$188.10
Purchase #3	$78.77	8.349%	$85.3465	$85.35	$85.35	$85.30
Purchase #4	$69.92	11.832%	$78.1929	$78.19	$78.20	$78.20
Purchase #5	$176.69	9.496%	$193.4685	$193.47	$193.45	$193.50
Purchase #6	$78.89	8.616%	$85.6872	$85.69	$85.70	$85.70
Purchase #7	$19.31	6.199%	$20.507	$20.51	$20.50	$20.50
7 purchase totals =	$620.23		$680.9622	$680.97	$680.95	$680.90