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	$31.81	6.535%	$33.8888	$33.89	$33.90	$33.90
Purchase #2	$16.92	9.607%	$18.5455	$18.55	$18.55	$18.50
Purchase #3	$41.89	12.776%	$47.2419	$47.24	$47.25	$47.20
Purchase #4	$28.61	11.830%	$31.9946	$31.99	$32.00	$32.00
Purchase #5	$158.50	5.294%	$166.891	$166.89	$166.90	$166.90
Purchase #6	$32.95	11.376%	$36.6984	$36.70	$36.70	$36.70
Purchase #7	$48.41	11.120%	$53.7932	$53.79	$53.80	$53.80
7 purchase totals =	$359.09		$389.0534	$389.05	$389.10	$389.00