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	$11.98	12.787%	$13.5119	$13.51	$13.50	$13.50
Purchase #2	$187.94	5.464%	$198.209	$198.21	$198.20	$198.20
Purchase #3	$41.74	3.830%	$43.3386	$43.34	$43.35	$43.30
Purchase #4	$73.34	6.381%	$78.0198	$78.02	$78.00	$78.00
Purchase #5	$143.42	3.346%	$148.2188	$148.22	$148.20	$148.20
Purchase #6	$67.27	9.737%	$73.8201	$73.82	$73.80	$73.80
Purchase #7	$147.28	7.680%	$158.5911	$158.59	$158.60	$158.60
7 purchase totals =	$672.97		$713.7093	$713.71	$713.65	$713.60