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	$247.66	13.216%	$280.3907	$280.39	$280.40	$280.40
Purchase #2	$238.88	5.402%	$251.7843	$251.78	$251.80	$251.80
Purchase #3	$181.47	8.356%	$196.6336	$196.63	$196.65	$196.60
Purchase #4	$231.76	9.832%	$254.5466	$254.55	$254.55	$254.50
Purchase #5	$72.43	5.456%	$76.3818	$76.38	$76.40	$76.40
Purchase #6	$210.80	5.626%	$222.6596	$222.66	$222.65	$222.70
Purchase #7	$113.26	9.593%	$124.125	$124.13	$124.15	$124.10
7 purchase totals =	$1,296.26		$1,406.5216	$1,406.52	$1,406.60	$1,406.50