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	$97.40	8.142%	$105.3303	$105.33	$105.35	$105.30
Purchase #2	$198.47	10.374%	$219.0593	$219.06	$219.05	$219.10
Purchase #3	$96.43	7.600%	$103.7587	$103.76	$103.75	$103.80
Purchase #4	$239.89	12.543%	$269.9794	$269.98	$270.00	$270.00
Purchase #5	$78.81	4.163%	$82.0909	$82.09	$82.10	$82.10
Purchase #6	$43.89	9.746%	$48.1675	$48.17	$48.15	$48.20
Purchase #7	$50.99	9.778%	$55.9758	$55.98	$56.00	$56.00
7 purchase totals =	$805.88		$884.3619	$884.37	$884.40	$884.50