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	$230.96	5.831%	$244.4273	$244.43	$244.45	$244.40
Purchase #2	$128.71	12.855%	$145.2557	$145.26	$145.25	$145.30
Purchase #3	$119.74	6.712%	$127.7769	$127.78	$127.80	$127.80
Purchase #4	$142.94	11.217%	$158.9736	$158.97	$158.95	$159.00
Purchase #5	$237.89	9.684%	$260.9273	$260.93	$260.95	$260.90
Purchase #6	$8.89	12.766%	$10.0249	$10.02	$10.00	$10.00
Purchase #7	$136.41	5.738%	$144.2372	$144.24	$144.25	$144.20
7 purchase totals =	$1,005.54		$1,091.6229	$1,091.63	$1,091.65	$1,091.60