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	$249.89	10.790%	$276.8531	$276.85	$276.85	$276.90
Purchase #2	$232.93	12.727%	$262.575	$262.58	$262.60	$262.60
Purchase #3	$150.35	3.272%	$155.2695	$155.27	$155.25	$155.30
Purchase #4	$65.38	11.174%	$72.6856	$72.69	$72.70	$72.70
Purchase #5	$156.81	6.692%	$167.3037	$167.30	$167.30	$167.30
Purchase #6	$17.40	9.408%	$19.037	$19.04	$19.05	$19.00
Purchase #7	$135.89	5.542%	$143.421	$143.42	$143.40	$143.40
7 purchase totals =	$1,008.65		$1,097.1449	$1,097.15	$1,097.15	$1,097.20