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	$9.89	13.507%	$11.2258	$11.23	$11.25	$11.20
Purchase #2	$52.36	12.780%	$59.0516	$59.05	$59.05	$59.10
Purchase #3	$101.72	7.510%	$109.3592	$109.36	$109.35	$109.40
Purchase #4	$244.75	9.387%	$267.7247	$267.72	$267.70	$267.70
Purchase #5	$146.39	9.292%	$159.9926	$159.99	$160.00	$160.00
Purchase #6	$63.50	6.841%	$67.844	$67.84	$67.85	$67.80
Purchase #7	$46.29	12.542%	$52.0957	$52.10	$52.10	$52.10
7 purchase totals =	$664.90		$727.2936	$727.29	$727.30	$727.30