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	$107.43	7.798%	$115.8074	$115.81	$115.80	$115.80
Purchase #2	$7.32	3.546%	$7.5796	$7.58	$7.60	$7.60
Purchase #3	$171.29	5.673%	$181.0073	$181.01	$181.00	$181.00
Purchase #4	$205.58	9.679%	$225.4781	$225.48	$225.50	$225.50
Purchase #5	$59.65	3.397%	$61.6763	$61.68	$61.70	$61.70
Purchase #6	$80.63	10.449%	$89.055	$89.06	$89.05	$89.10
Purchase #7	$133.76	12.302%	$150.2152	$150.22	$150.20	$150.20
7 purchase totals =	$765.66		$830.8189	$830.84	$830.85	$830.90