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	$174.41	9.863%	$191.6121	$191.61	$191.60	$191.60
Purchase #2	$213.87	13.264%	$242.2377	$242.24	$242.25	$242.20
Purchase #3	$196.64	8.718%	$213.7831	$213.78	$213.80	$213.80
Purchase #4	$12.75	9.196%	$13.9225	$13.92	$13.90	$13.90
Purchase #5	$18.40	10.228%	$20.282	$20.28	$20.30	$20.30
Purchase #6	$119.64	6.220%	$127.0816	$127.08	$127.10	$127.10
Purchase #7	$20.76	6.180%	$22.043	$22.04	$22.05	$22.00
7 purchase totals =	$756.47		$830.9620	$830.95	$831.00	$830.90