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	$120.84	10.338%	$133.3324	$133.33	$133.35	$133.30
Purchase #2	$56.78	9.645%	$62.2564	$62.26	$62.25	$62.30
Purchase #3	$59.66	12.556%	$67.1509	$67.15	$67.15	$67.20
Purchase #4	$15.98	13.261%	$18.0991	$18.10	$18.10	$18.10
Purchase #5	$73.32	13.308%	$83.0774	$83.08	$83.10	$83.10
Purchase #6	$72.30	12.315%	$81.2037	$81.20	$81.20	$81.20
Purchase #7	$132.94	13.818%	$151.3096	$151.31	$151.30	$151.30
7 purchase totals =	$531.82		$596.4295	$596.43	$596.45	$596.50