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	$147.79	6.293%	$157.0904	$157.09	$157.10	$157.10
Purchase #2	$247.33	13.264%	$280.1359	$280.14	$280.15	$280.10
Purchase #3	$49.30	7.517%	$53.0059	$53.01	$53.00	$53.00
Purchase #4	$63.40	12.862%	$71.5545	$71.55	$71.55	$71.60
Purchase #5	$74.63	10.532%	$82.49	$82.49	$82.50	$82.50
Purchase #6	$95.58	5.196%	$100.5463	$100.55	$100.55	$100.50
Purchase #7	$224.73	4.386%	$234.5867	$234.59	$234.60	$234.60
7 purchase totals =	$902.76		$979.4097	$979.42	$979.45	$979.40