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	$51.37	9.144%	$56.0673	$56.07	$56.05	$56.10
Purchase #2	$111.85	4.726%	$117.136	$117.14	$117.15	$117.10
Purchase #3	$165.50	9.536%	$181.2821	$181.28	$181.30	$181.30
Purchase #4	$36.47	13.505%	$41.3953	$41.40	$41.40	$41.40
Purchase #5	$165.71	13.726%	$188.4554	$188.46	$188.45	$188.50
Purchase #6	$225.96	10.725%	$250.1942	$250.19	$250.20	$250.20
Purchase #7	$124.38	10.597%	$137.5605	$137.56	$137.55	$137.60
7 purchase totals =	$881.24		$972.0908	$972.10	$972.10	$972.20