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	$20.25	12.186%	$22.7177	$22.72	$22.70	$22.70
Purchase #2	$125.78	11.772%	$140.5868	$140.59	$140.60	$140.60
Purchase #3	$180.35	11.338%	$200.7981	$200.80	$200.80	$200.80
Purchase #4	$240.76	8.830%	$262.0191	$262.02	$262.00	$262.00
Purchase #5	$242.76	7.642%	$261.3117	$261.31	$261.30	$261.30
Purchase #6	$98.31	4.573%	$102.8057	$102.81	$102.80	$102.80
Purchase #7	$56.55	4.772%	$59.2486	$59.25	$59.25	$59.20
7 purchase totals =	$964.76		$1,049.4877	$1,049.50	$1,049.45	$1,049.40