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	$248.90	13.127%	$281.5731	$281.57	$281.55	$281.60
Purchase #2	$62.29	5.776%	$65.8879	$65.89	$65.90	$65.90
Purchase #3	$173.35	7.138%	$185.7237	$185.72	$185.70	$185.70
Purchase #4	$106.70	6.407%	$113.5363	$113.54	$113.55	$113.50
Purchase #5	$21.52	13.347%	$24.3923	$24.39	$24.40	$24.40
Purchase #6	$79.95	8.422%	$86.6834	$86.68	$86.70	$86.70
Purchase #7	$243.57	7.861%	$262.717	$262.72	$262.70	$262.70
7 purchase totals =	$936.28		$1,020.5137	$1,020.51	$1,020.50	$1,020.50