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	$18.62	10.712%	$20.6146	$20.61	$20.60	$20.60
Purchase #2	$174.78	13.295%	$198.017	$198.02	$198.00	$198.00
Purchase #3	$72.63	7.667%	$78.1985	$78.20	$78.20	$78.20
Purchase #4	$217.49	11.423%	$242.3339	$242.33	$242.35	$242.30
Purchase #5	$52.69	9.548%	$57.7208	$57.72	$57.70	$57.70
Purchase #6	$18.72	4.522%	$19.5665	$19.57	$19.55	$19.60
Purchase #7	$127.33	12.799%	$143.627	$143.63	$143.65	$143.60
7 purchase totals =	$682.26		$760.0783	$760.08	$760.05	$760.00