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	$236.87	8.421%	$256.8168	$256.82	$256.80	$256.80
Purchase #2	$247.75	13.235%	$280.5397	$280.54	$280.55	$280.50
Purchase #3	$178.62	11.370%	$198.9291	$198.93	$198.95	$198.90
Purchase #4	$141.65	9.830%	$155.5742	$155.57	$155.55	$155.60
Purchase #5	$171.41	8.420%	$185.8427	$185.84	$185.85	$185.80
Purchase #6	$65.34	8.651%	$70.9926	$70.99	$71.00	$71.00
Purchase #7	$120.90	8.837%	$131.5839	$131.58	$131.60	$131.60
7 purchase totals =	$1,162.54		$1,280.2790	$1,280.27	$1,280.30	$1,280.20