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	$151.53	10.735%	$167.7967	$167.80	$167.80	$167.80
Purchase #2	$137.38	4.730%	$143.8781	$143.88	$143.90	$143.90
Purchase #3	$247.31	11.475%	$275.6888	$275.69	$275.70	$275.70
Purchase #4	$49.35	11.105%	$54.8303	$54.83	$54.85	$54.80
Purchase #5	$243.97	9.804%	$267.8888	$267.89	$267.90	$267.90
Purchase #6	$19.32	10.411%	$21.3314	$21.33	$21.35	$21.30
Purchase #7	$23.75	3.333%	$24.5416	$24.54	$24.55	$24.50
7 purchase totals =	$872.61		$955.9557	$955.96	$956.05	$955.90