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	$36.92	10.766%	$40.8948	$40.89	$40.90	$40.90
Purchase #2	$182.80	3.598%	$189.3771	$189.38	$189.40	$189.40
Purchase #3	$31.69	11.419%	$35.3087	$35.31	$35.30	$35.30
Purchase #4	$235.86	12.848%	$266.1633	$266.16	$266.15	$266.20
Purchase #5	$154.51	3.863%	$160.4787	$160.48	$160.50	$160.50
Purchase #6	$161.48	13.636%	$183.4994	$183.50	$183.50	$183.50
Purchase #7	$101.72	6.185%	$108.0114	$108.01	$108.00	$108.00
7 purchase totals =	$904.98		$983.7334	$983.73	$983.75	$983.80