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	$51.66	6.487%	$55.0112	$55.01	$55.00	$55.00
Purchase #2	$119.60	8.759%	$130.0758	$130.08	$130.10	$130.10
Purchase #3	$137.26	13.229%	$155.4181	$155.42	$155.40	$155.40
Purchase #4	$79.65	4.381%	$83.1395	$83.14	$83.15	$83.10
Purchase #5	$69.53	4.602%	$72.7298	$72.73	$72.75	$72.70
Purchase #6	$153.38	7.427%	$164.7715	$164.77	$164.75	$164.80
Purchase #7	$132.31	5.431%	$139.4958	$139.50	$139.50	$139.50
7 purchase totals =	$743.39		$800.6417	$800.65	$800.65	$800.60