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	$164.65	5.801%	$174.2013	$174.20	$174.20	$174.20
Purchase #2	$81.63	9.586%	$89.4551	$89.46	$89.45	$89.50
Purchase #3	$151.94	5.610%	$160.4638	$160.46	$160.45	$160.50
Purchase #4	$95.64	11.704%	$106.8337	$106.83	$106.85	$106.80
Purchase #5	$178.45	12.238%	$200.2887	$200.29	$200.30	$200.30
Purchase #6	$123.52	5.384%	$130.1703	$130.17	$130.15	$130.20
Purchase #7	$211.32	6.500%	$225.0558	$225.06	$225.05	$225.10
7 purchase totals =	$1,007.15		$1,086.4687	$1,086.47	$1,086.45	$1,086.60