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	$152.94	7.573%	$164.5221	$164.52	$164.50	$164.50
Purchase #2	$241.56	12.708%	$272.2574	$272.26	$272.25	$272.30
Purchase #3	$47.71	12.752%	$53.794	$53.79	$53.80	$53.80
Purchase #4	$93.60	5.494%	$98.7424	$98.74	$98.75	$98.70
Purchase #5	$20.89	6.792%	$22.3088	$22.31	$22.30	$22.30
Purchase #6	$96.71	7.321%	$103.7901	$103.79	$103.80	$103.80
Purchase #7	$107.71	10.365%	$118.8741	$118.87	$118.85	$118.90
7 purchase totals =	$761.12		$834.2889	$834.28	$834.25	$834.30