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	$99.76	3.534%	$103.2855	$103.29	$103.30	$103.30
Purchase #2	$39.25	8.738%	$42.6797	$42.68	$42.70	$42.70
Purchase #3	$38.59	11.711%	$43.1093	$43.11	$43.10	$43.10
Purchase #4	$60.75	13.161%	$68.7453	$68.75	$68.75	$68.70
Purchase #5	$61.75	6.688%	$65.8798	$65.88	$65.90	$65.90
Purchase #6	$125.90	10.780%	$139.472	$139.47	$139.45	$139.50
Purchase #7	$116.84	12.807%	$131.8037	$131.80	$131.80	$131.80
7 purchase totals =	$542.84		$594.9753	$594.98	$595.00	$595.00