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	$22.44	6.373%	$23.8701	$23.87	$23.85	$23.90
Purchase #2	$104.87	11.627%	$117.0632	$117.06	$117.05	$117.10
Purchase #3	$40.90	10.325%	$45.1229	$45.12	$45.10	$45.10
Purchase #4	$60.79	8.615%	$66.0271	$66.03	$66.05	$66.00
Purchase #5	$26.71	11.529%	$29.7894	$29.79	$29.80	$29.80
Purchase #6	$76.72	5.401%	$80.8636	$80.86	$80.85	$80.90
Purchase #7	$75.47	3.564%	$78.1598	$78.16	$78.15	$78.20
7 purchase totals =	$407.90		$440.8961	$440.89	$440.85	$441.00