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	$243.55	13.238%	$275.7911	$275.79	$275.80	$275.80
Purchase #2	$134.75	7.786%	$145.2416	$145.24	$145.25	$145.20
Purchase #3	$17.61	5.535%	$18.5847	$18.58	$18.60	$18.60
Purchase #4	$113.30	13.749%	$128.8776	$128.88	$128.90	$128.90
Purchase #5	$214.29	12.457%	$240.9841	$240.98	$241.00	$241.00
Purchase #6	$44.78	12.181%	$50.2347	$50.23	$50.25	$50.20
Purchase #7	$200.89	10.207%	$221.3948	$221.39	$221.40	$221.40
7 purchase totals =	$969.17		$1,081.1086	$1,081.09	$1,081.20	$1,081.10