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	$14.38	10.775%	$15.9294	$15.93	$15.95	$15.90
Purchase #2	$241.81	11.790%	$270.3194	$270.32	$270.30	$270.30
Purchase #3	$19.76	5.289%	$20.8051	$20.81	$20.80	$20.80
Purchase #4	$196.88	3.412%	$203.5975	$203.60	$203.60	$203.60
Purchase #5	$12.69	6.612%	$13.5291	$13.53	$13.55	$13.50
Purchase #6	$47.50	9.569%	$52.0453	$52.05	$52.05	$52.00
Purchase #7	$80.45	13.844%	$91.5875	$91.59	$91.60	$91.60
7 purchase totals =	$613.47		$667.8133	$667.83	$667.85	$667.70