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	$90.43	4.860%	$94.8249	$94.82	$94.80	$94.80
Purchase #2	$69.45	13.186%	$78.6077	$78.61	$78.60	$78.60
Purchase #3	$31.64	5.761%	$33.4628	$33.46	$33.45	$33.50
Purchase #4	$124.51	10.721%	$137.8587	$137.86	$137.85	$137.90
Purchase #5	$76.77	9.274%	$83.8896	$83.89	$83.90	$83.90
Purchase #6	$108.69	11.255%	$120.9231	$120.92	$120.90	$120.90
Purchase #7	$42.54	11.365%	$47.3747	$47.37	$47.35	$47.40
7 purchase totals =	$544.03		$596.9415	$596.93	$596.85	$597.00