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	$86.47	4.620%	$90.4649	$90.46	$90.45	$90.50
Purchase #2	$86.72	7.116%	$92.891	$92.89	$92.90	$92.90
Purchase #3	$246.38	13.759%	$280.2794	$280.28	$280.30	$280.30
Purchase #4	$124.41	5.587%	$131.3608	$131.36	$131.35	$131.40
Purchase #5	$132.46	8.765%	$144.0701	$144.07	$144.05	$144.10
Purchase #6	$20.74	5.453%	$21.871	$21.87	$21.85	$21.90
Purchase #7	$103.79	6.526%	$110.5633	$110.56	$110.55	$110.60
7 purchase totals =	$800.97		$871.5005	$871.49	$871.45	$871.70