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	$20.61	10.308%	$22.7345	$22.73	$22.75	$22.70
Purchase #2	$248.61	12.812%	$280.4619	$280.46	$280.45	$280.50
Purchase #3	$71.28	9.759%	$78.2362	$78.24	$78.25	$78.20
Purchase #4	$74.66	9.605%	$81.8311	$81.83	$81.85	$81.80
Purchase #5	$238.48	7.739%	$256.936	$256.94	$256.95	$256.90
Purchase #6	$133.77	12.173%	$150.0538	$150.05	$150.05	$150.10
Purchase #7	$37.57	6.304%	$39.9384	$39.94	$39.95	$39.90
7 purchase totals =	$824.98		$910.1919	$910.19	$910.25	$910.10