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	$121.55	13.405%	$137.8438	$137.84	$137.85	$137.80
Purchase #2	$132.26	9.145%	$144.3552	$144.36	$144.35	$144.40
Purchase #3	$48.79	5.350%	$51.4003	$51.40	$51.40	$51.40
Purchase #4	$152.65	11.175%	$169.7086	$169.71	$169.70	$169.70
Purchase #5	$68.36	4.314%	$71.3091	$71.31	$71.30	$71.30
Purchase #6	$232.51	11.518%	$259.2905	$259.29	$259.30	$259.30
Purchase #7	$181.47	13.274%	$205.5583	$205.56	$205.55	$205.60
7 purchase totals =	$937.59		$1,039.4658	$1,039.47	$1,039.45	$1,039.50