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	$171.36	6.827%	$183.0587	$183.06	$183.05	$183.10
Purchase #2	$64.36	5.377%	$67.8206	$67.82	$67.80	$67.80
Purchase #3	$151.79	8.444%	$164.6071	$164.61	$164.60	$164.60
Purchase #4	$28.82	12.732%	$32.4894	$32.49	$32.50	$32.50
Purchase #5	$69.34	10.854%	$76.8662	$76.87	$76.85	$76.90
Purchase #6	$28.67	13.405%	$32.5132	$32.51	$32.50	$32.50
Purchase #7	$224.28	8.337%	$242.9782	$242.98	$243.00	$243.00
7 purchase totals =	$738.62		$800.3334	$800.34	$800.30	$800.40