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	$247.75	3.541%	$256.5228	$256.52	$256.50	$256.50
Purchase #2	$70.73	8.742%	$76.9132	$76.91	$76.90	$76.90
Purchase #3	$7.28	8.789%	$7.9198	$7.92	$7.90	$7.90
Purchase #4	$68.70	5.272%	$72.3219	$72.32	$72.30	$72.30
Purchase #5	$10.96	5.260%	$11.5365	$11.54	$11.55	$11.50
Purchase #6	$111.47	4.187%	$116.1372	$116.14	$116.15	$116.10
Purchase #7	$47.67	9.181%	$52.0466	$52.05	$52.05	$52.00
7 purchase totals =	$564.56		$593.3980	$593.40	$593.35	$593.20