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	$209.40	12.462%	$235.4954	$235.50	$235.50	$235.50
Purchase #2	$124.60	11.421%	$138.8306	$138.83	$138.85	$138.80
Purchase #3	$200.91	9.850%	$220.6996	$220.70	$220.70	$220.70
Purchase #4	$135.46	6.384%	$144.1078	$144.11	$144.10	$144.10
Purchase #5	$167.83	9.263%	$183.3761	$183.38	$183.40	$183.40
Purchase #6	$106.76	4.192%	$111.2354	$111.24	$111.25	$111.20
Purchase #7	$63.49	3.148%	$65.4887	$65.49	$65.50	$65.50
7 purchase totals =	$1,008.45		$1,099.2336	$1,099.25	$1,099.30	$1,099.20