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	$226.57	7.863%	$244.3852	$244.39	$244.40	$244.40
Purchase #2	$98.87	10.638%	$109.3878	$109.39	$109.40	$109.40
Purchase #3	$87.66	12.136%	$98.2984	$98.30	$98.30	$98.30
Purchase #4	$59.52	11.228%	$66.2029	$66.20	$66.20	$66.20
Purchase #5	$140.76	8.761%	$153.092	$153.09	$153.10	$153.10
Purchase #6	$106.35	10.687%	$117.7156	$117.72	$117.70	$117.70
Purchase #7	$227.33	10.376%	$250.9178	$250.92	$250.90	$250.90
7 purchase totals =	$947.06		$1,039.9997	$1,040.01	$1,040.00	$1,040.00