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	$17.28	5.426%	$18.2176	$18.22	$18.20	$18.20
Purchase #2	$89.80	8.863%	$97.759	$97.76	$97.75	$97.80
Purchase #3	$195.88	11.771%	$218.937	$218.94	$218.95	$218.90
Purchase #4	$63.64	13.832%	$72.4427	$72.44	$72.45	$72.40
Purchase #5	$241.60	6.171%	$256.5091	$256.51	$256.50	$256.50
Purchase #6	$17.35	5.326%	$18.2741	$18.27	$18.25	$18.30
Purchase #7	$149.35	4.761%	$156.4606	$156.46	$156.45	$156.50
7 purchase totals =	$774.90		$838.6001	$838.60	$838.55	$838.60