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	$111.69	4.369%	$116.5697	$116.57	$116.55	$116.60
Purchase #2	$138.98	10.340%	$153.3505	$153.35	$153.35	$153.40
Purchase #3	$58.85	8.474%	$63.8369	$63.84	$63.85	$63.80
Purchase #4	$223.53	3.459%	$231.2619	$231.26	$231.25	$231.30
Purchase #5	$229.85	12.503%	$258.5881	$258.59	$258.60	$258.60
Purchase #6	$247.38	13.530%	$280.8505	$280.85	$280.85	$280.90
Purchase #7	$32.37	3.312%	$33.4421	$33.44	$33.45	$33.40
7 purchase totals =	$1,042.65		$1,137.8997	$1,137.90	$1,137.90	$1,138.00