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	$38.73	10.506%	$42.799	$42.80	$42.80	$42.80
Purchase #2	$37.45	12.672%	$42.1957	$42.20	$42.20	$42.20
Purchase #3	$241.70	5.452%	$254.8775	$254.88	$254.90	$254.90
Purchase #4	$98.72	13.429%	$111.9771	$111.98	$112.00	$112.00
Purchase #5	$99.26	5.657%	$104.8751	$104.88	$104.90	$104.90
Purchase #6	$138.54	4.847%	$145.255	$145.26	$145.25	$145.30
Purchase #7	$222.63	5.506%	$234.888	$234.89	$234.90	$234.90
7 purchase totals =	$877.03		$936.8674	$936.89	$936.95	$937.00