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	$180.72	5.424%	$190.5223	$190.52	$190.50	$190.50
Purchase #2	$236.67	8.767%	$257.4189	$257.42	$257.40	$257.40
Purchase #3	$227.52	12.250%	$255.3912	$255.39	$255.40	$255.40
Purchase #4	$240.44	9.124%	$262.3777	$262.38	$262.40	$262.40
Purchase #5	$66.92	3.165%	$69.038	$69.04	$69.05	$69.00
Purchase #6	$35.64	8.743%	$38.756	$38.76	$38.75	$38.80
Purchase #7	$60.98	10.342%	$67.2866	$67.29	$67.30	$67.30
7 purchase totals =	$1,048.89		$1,140.7907	$1,140.80	$1,140.80	$1,140.80