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	$214.44	3.776%	$222.5373	$222.54	$222.55	$222.50
Purchase #2	$28.57	12.578%	$32.1635	$32.16	$32.15	$32.20
Purchase #3	$221.67	12.486%	$249.3477	$249.35	$249.35	$249.30
Purchase #4	$248.87	12.601%	$280.2301	$280.23	$280.25	$280.20
Purchase #5	$55.86	5.658%	$59.0206	$59.02	$59.00	$59.00
Purchase #6	$35.57	5.835%	$37.6455	$37.65	$37.65	$37.60
Purchase #7	$103.46	4.510%	$108.126	$108.13	$108.15	$108.10
7 purchase totals =	$908.44		$989.0707	$989.08	$989.10	$988.90