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	$114.29	3.723%	$118.545	$118.55	$118.55	$118.50
Purchase #2	$107.96	9.823%	$118.5649	$118.56	$118.55	$118.60
Purchase #3	$198.64	10.168%	$218.8377	$218.84	$218.85	$218.80
Purchase #4	$139.52	9.311%	$152.5107	$152.51	$152.50	$152.50
Purchase #5	$211.64	3.247%	$218.512	$218.51	$218.50	$218.50
Purchase #6	$84.26	6.723%	$89.9248	$89.92	$89.90	$89.90
Purchase #7	$80.64	3.869%	$83.76	$83.76	$83.75	$83.80
7 purchase totals =	$936.95		$1,000.6551	$1,000.65	$1,000.60	$1,000.60