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	$212.47	5.638%	$224.4491	$224.45	$224.45	$224.40
Purchase #2	$247.58	13.279%	$280.4561	$280.46	$280.45	$280.50
Purchase #3	$123.28	11.643%	$137.6335	$137.63	$137.65	$137.60
Purchase #4	$59.66	10.854%	$66.1355	$66.14	$66.15	$66.10
Purchase #5	$100.49	9.222%	$109.7572	$109.76	$109.75	$109.80
Purchase #6	$217.36	10.192%	$239.5133	$239.51	$239.50	$239.50
Purchase #7	$213.84	9.243%	$233.6052	$233.61	$233.60	$233.60
7 purchase totals =	$1,174.68		$1,291.5499	$1,291.56	$1,291.55	$1,291.50