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	$244.63	12.358%	$274.8614	$274.86	$274.85	$274.90
Purchase #2	$200.41	11.547%	$223.5513	$223.55	$223.55	$223.60
Purchase #3	$248.68	12.785%	$280.4737	$280.47	$280.45	$280.50
Purchase #4	$80.91	3.761%	$83.953	$83.95	$83.95	$84.00
Purchase #5	$211.65	5.175%	$222.6029	$222.60	$222.60	$222.60
Purchase #6	$131.97	12.323%	$148.2327	$148.23	$148.25	$148.20
Purchase #7	$197.25	13.367%	$223.6164	$223.62	$223.60	$223.60
7 purchase totals =	$1,315.50		$1,457.2914	$1,457.28	$1,457.25	$1,457.40