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	$106.92	3.245%	$110.3896	$110.39	$110.40	$110.40
Purchase #2	$209.68	11.836%	$234.4977	$234.50	$234.50	$234.50
Purchase #3	$34.35	9.636%	$37.66	$37.66	$37.65	$37.70
Purchase #4	$141.83	13.571%	$161.0777	$161.08	$161.10	$161.10
Purchase #5	$141.67	9.766%	$155.5055	$155.51	$155.50	$155.50
Purchase #6	$136.81	4.447%	$142.8939	$142.89	$142.90	$142.90
Purchase #7	$229.94	11.231%	$255.7646	$255.76	$255.75	$255.80
7 purchase totals =	$1,001.20		$1,097.7890	$1,097.79	$1,097.80	$1,097.90