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	$45.32	7.590%	$48.7598	$48.76	$48.75	$48.80
Purchase #2	$130.99	10.152%	$144.2881	$144.29	$144.30	$144.30
Purchase #3	$239.78	3.223%	$247.5081	$247.51	$247.50	$247.50
Purchase #4	$168.97	12.230%	$189.635	$189.64	$189.65	$189.60
Purchase #5	$123.52	6.442%	$131.4772	$131.48	$131.50	$131.50
Purchase #6	$23.92	10.195%	$26.3586	$26.36	$26.35	$26.40
Purchase #7	$72.44	13.402%	$82.1484	$82.15	$82.15	$82.10
7 purchase totals =	$804.94		$870.1752	$870.19	$870.20	$870.20