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	$62.50	9.510%	$68.4438	$68.44	$68.45	$68.40
Purchase #2	$85.78	11.709%	$95.824	$95.82	$95.80	$95.80
Purchase #3	$131.74	6.690%	$140.5534	$140.55	$140.55	$140.60
Purchase #4	$45.42	12.554%	$51.122	$51.12	$51.10	$51.10
Purchase #5	$93.43	6.719%	$99.7076	$99.71	$99.70	$99.70
Purchase #6	$40.29	8.657%	$43.7779	$43.78	$43.80	$43.80
Purchase #7	$42.37	12.386%	$47.6179	$47.62	$47.60	$47.60
7 purchase totals =	$501.53		$547.0466	$547.04	$547.00	$547.00