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	$78.86	4.622%	$82.5049	$82.50	$82.50	$82.50
Purchase #2	$46.97	7.654%	$50.5651	$50.57	$50.55	$50.60
Purchase #3	$12.39	10.161%	$13.6489	$13.65	$13.65	$13.60
Purchase #4	$94.92	13.678%	$107.9032	$107.90	$107.90	$107.90
Purchase #5	$36.48	5.260%	$38.3988	$38.40	$38.40	$38.40
Purchase #6	$96.51	4.429%	$100.7844	$100.78	$100.80	$100.80
Purchase #7	$238.38	7.509%	$256.28	$256.28	$256.30	$256.30
7 purchase totals =	$604.51		$650.0853	$650.08	$650.10	$650.10