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	$124.65	11.850%	$139.421	$139.42	$139.40	$139.40
Purchase #2	$214.25	3.768%	$222.3229	$222.32	$222.30	$222.30
Purchase #3	$233.72	12.355%	$262.5961	$262.60	$262.60	$262.60
Purchase #4	$230.85	6.133%	$245.008	$245.01	$245.00	$245.00
Purchase #5	$184.27	8.386%	$199.7229	$199.72	$199.70	$199.70
Purchase #6	$234.39	12.401%	$263.4567	$263.46	$263.45	$263.50
Purchase #7	$7.65	10.475%	$8.4513	$8.45	$8.45	$8.50
7 purchase totals =	$1,229.78		$1,340.9789	$1,340.98	$1,340.90	$1,341.00