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	$234.92	12.531%	$264.3578	$264.36	$264.35	$264.40
Purchase #2	$123.30	7.122%	$132.0814	$132.08	$132.10	$132.10
Purchase #3	$122.82	7.242%	$131.7146	$131.71	$131.70	$131.70
Purchase #4	$185.67	10.811%	$205.7428	$205.74	$205.75	$205.70
Purchase #5	$146.60	9.201%	$160.0887	$160.09	$160.10	$160.10
Purchase #6	$142.32	11.118%	$158.1431	$158.14	$158.15	$158.10
Purchase #7	$76.25	3.532%	$78.9432	$78.94	$78.95	$78.90
7 purchase totals =	$1,031.88		$1,131.0716	$1,131.06	$1,131.10	$1,131.00