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	$50.70	10.793%	$56.1721	$56.17	$56.15	$56.20
Purchase #2	$150.27	4.223%	$156.6159	$156.62	$156.60	$156.60
Purchase #3	$128.81	9.858%	$141.5081	$141.51	$141.50	$141.50
Purchase #4	$143.36	7.369%	$153.9242	$153.92	$153.90	$153.90
Purchase #5	$53.48	9.330%	$58.4697	$58.47	$58.45	$58.50
Purchase #6	$125.91	12.770%	$141.9887	$141.99	$142.00	$142.00
Purchase #7	$126.28	3.776%	$131.0483	$131.05	$131.05	$131.00
7 purchase totals =	$778.81		$839.7270	$839.73	$839.65	$839.70