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	$123.28	6.600%	$131.4165	$131.42	$131.40	$131.40
Purchase #2	$30.68	10.496%	$33.9002	$33.90	$33.90	$33.90
Purchase #3	$139.30	5.186%	$146.5241	$146.52	$146.50	$146.50
Purchase #4	$119.36	12.349%	$134.0998	$134.10	$134.10	$134.10
Purchase #5	$120.55	11.654%	$134.5989	$134.60	$134.60	$134.60
Purchase #6	$236.35	5.530%	$249.4202	$249.42	$249.40	$249.40
Purchase #7	$177.25	12.217%	$198.9046	$198.90	$198.90	$198.90
7 purchase totals =	$946.77		$1,028.8643	$1,028.86	$1,028.80	$1,028.80