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	$104.41	7.557%	$112.3003	$112.30	$112.30	$112.30
Purchase #2	$63.50	11.507%	$70.8069	$70.81	$70.80	$70.80
Purchase #3	$141.62	10.772%	$156.8753	$156.88	$156.90	$156.90
Purchase #4	$208.96	9.336%	$228.4685	$228.47	$228.45	$228.50
Purchase #5	$150.60	12.135%	$168.8753	$168.88	$168.90	$168.90
Purchase #6	$12.59	3.662%	$13.051	$13.05	$13.05	$13.10
Purchase #7	$226.28	12.419%	$254.3817	$254.38	$254.40	$254.40
7 purchase totals =	$907.96		$1,004.7590	$1,004.77	$1,004.80	$1,004.90