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	$249.79	4.595%	$261.2679	$261.27	$261.25	$261.30
Purchase #2	$178.64	12.167%	$200.3751	$200.38	$200.40	$200.40
Purchase #3	$248.99	13.561%	$282.7555	$282.76	$282.75	$282.80
Purchase #4	$246.96	13.535%	$280.386	$280.39	$280.40	$280.40
Purchase #5	$105.82	3.250%	$109.2592	$109.26	$109.25	$109.30
Purchase #6	$139.30	3.292%	$143.8858	$143.89	$143.90	$143.90
Purchase #7	$62.98	12.286%	$70.7177	$70.72	$70.70	$70.70
7 purchase totals =	$1,232.48		$1,348.6472	$1,348.67	$1,348.65	$1,348.80