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	$142.82	13.770%	$162.4863	$162.49	$162.50	$162.50
Purchase #2	$249.64	13.212%	$282.6224	$282.62	$282.60	$282.60
Purchase #3	$123.60	12.678%	$139.27	$139.27	$139.25	$139.30
Purchase #4	$40.74	5.843%	$43.1204	$43.12	$43.10	$43.10
Purchase #5	$130.27	11.159%	$144.8068	$144.81	$144.80	$144.80
Purchase #6	$42.58	5.142%	$44.7695	$44.77	$44.75	$44.80
Purchase #7	$7.82	7.512%	$8.4074	$8.41	$8.40	$8.40
7 purchase totals =	$737.47		$825.4828	$825.49	$825.40	$825.50