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	$136.57	11.845%	$152.7467	$152.75	$152.75	$152.70
Purchase #2	$222.89	9.632%	$244.3588	$244.36	$244.35	$244.40
Purchase #3	$143.92	8.326%	$155.9028	$155.90	$155.90	$155.90
Purchase #4	$6.50	11.235%	$7.2303	$7.23	$7.25	$7.20
Purchase #5	$44.86	13.850%	$51.0731	$51.07	$51.05	$51.10
Purchase #6	$55.83	3.312%	$57.6791	$57.68	$57.70	$57.70
Purchase #7	$97.71	13.714%	$111.1099	$111.11	$111.10	$111.10
7 purchase totals =	$708.28		$780.1007	$780.10	$780.10	$780.10