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	$27.58	10.560%	$30.4924	$30.49	$30.50	$30.50
Purchase #2	$177.60	10.413%	$196.0935	$196.09	$196.10	$196.10
Purchase #3	$141.31	7.706%	$152.1993	$152.20	$152.20	$152.20
Purchase #4	$192.38	12.361%	$216.1601	$216.16	$216.15	$216.20
Purchase #5	$89.72	11.667%	$100.1876	$100.19	$100.20	$100.20
Purchase #6	$233.60	10.781%	$258.7844	$258.78	$258.80	$258.80
Purchase #7	$208.89	9.477%	$228.6865	$228.69	$228.70	$228.70
7 purchase totals =	$1,071.08		$1,182.6038	$1,182.60	$1,182.65	$1,182.70