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	$142.56	4.393%	$148.8227	$148.82	$148.80	$148.80
Purchase #2	$17.33	8.567%	$18.8147	$18.81	$18.80	$18.80
Purchase #3	$126.45	11.583%	$141.0967	$141.10	$141.10	$141.10
Purchase #4	$240.97	11.593%	$268.9057	$268.91	$268.90	$268.90
Purchase #5	$245.75	6.708%	$262.2349	$262.23	$262.25	$262.20
Purchase #6	$19.99	8.353%	$21.6598	$21.66	$21.65	$21.70
Purchase #7	$112.38	13.814%	$127.9042	$127.90	$127.90	$127.90
7 purchase totals =	$905.43		$989.4387	$989.43	$989.40	$989.40