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	$38.80	4.363%	$40.4928	$40.49	$40.50	$40.50
Purchase #2	$247.93	7.292%	$266.0091	$266.01	$266.00	$266.00
Purchase #3	$63.94	6.433%	$68.0533	$68.05	$68.05	$68.10
Purchase #4	$174.78	9.564%	$191.496	$191.50	$191.50	$191.50
Purchase #5	$8.62	8.801%	$9.3786	$9.38	$9.40	$9.40
Purchase #6	$65.42	7.348%	$70.2271	$70.23	$70.25	$70.20
Purchase #7	$85.73	4.848%	$89.8862	$89.89	$89.90	$89.90
7 purchase totals =	$685.22		$735.5431	$735.55	$735.60	$735.60