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	$65.76	10.229%	$72.4866	$72.49	$72.50	$72.50
Purchase #2	$236.36	12.298%	$265.4276	$265.43	$265.45	$265.40
Purchase #3	$72.50	10.415%	$80.0509	$80.05	$80.05	$80.10
Purchase #4	$86.28	8.611%	$93.7096	$93.71	$93.70	$93.70
Purchase #5	$67.28	6.287%	$71.5099	$71.51	$71.50	$71.50
Purchase #6	$132.83	7.835%	$143.2372	$143.24	$143.25	$143.20
Purchase #7	$66.71	12.639%	$75.1415	$75.14	$75.15	$75.10
7 purchase totals =	$727.72		$801.5633	$801.57	$801.60	$801.50