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	$53.37	7.528%	$57.3877	$57.39	$57.40	$57.40
Purchase #2	$92.77	6.465%	$98.7676	$98.77	$98.75	$98.80
Purchase #3	$106.86	4.386%	$111.5469	$111.55	$111.55	$111.50
Purchase #4	$113.47	4.183%	$118.2165	$118.22	$118.20	$118.20
Purchase #5	$162.35	11.659%	$181.2784	$181.28	$181.30	$181.30
Purchase #6	$226.41	10.384%	$249.9204	$249.92	$249.90	$249.90
Purchase #7	$134.84	3.688%	$139.8129	$139.81	$139.80	$139.80
7 purchase totals =	$890.07		$956.9304	$956.94	$956.90	$956.90