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	$17.78	3.170%	$18.3436	$18.34	$18.35	$18.30
Purchase #2	$157.61	9.375%	$172.3859	$172.39	$172.40	$172.40
Purchase #3	$90.51	13.816%	$103.0149	$103.01	$103.00	$103.00
Purchase #4	$5.29	10.716%	$5.8569	$5.86	$5.85	$5.90
Purchase #5	$181.58	4.147%	$189.1101	$189.11	$189.10	$189.10
Purchase #6	$144.91	3.590%	$150.1123	$150.11	$150.10	$150.10
Purchase #7	$87.88	7.455%	$94.4315	$94.43	$94.45	$94.40
7 purchase totals =	$685.56		$733.2552	$733.25	$733.25	$733.20