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	$231.74	3.843%	$240.6458	$240.65	$240.65	$240.60
Purchase #2	$56.37	6.485%	$60.0256	$60.03	$60.05	$60.00
Purchase #3	$35.39	13.146%	$40.0424	$40.04	$40.05	$40.00
Purchase #4	$180.72	6.767%	$192.9493	$192.95	$192.95	$192.90
Purchase #5	$212.43	7.548%	$228.4642	$228.46	$228.45	$228.50
Purchase #6	$198.63	8.655%	$215.8214	$215.82	$215.80	$215.80
Purchase #7	$101.27	10.407%	$111.8092	$111.81	$111.80	$111.80
7 purchase totals =	$1,016.55		$1,089.7579	$1,089.76	$1,089.75	$1,089.60