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	$145.38	3.704%	$150.7649	$150.76	$150.75	$150.80
Purchase #2	$51.32	5.280%	$54.0297	$54.03	$54.05	$54.00
Purchase #3	$155.59	4.499%	$162.59	$162.59	$162.60	$162.60
Purchase #4	$50.41	11.426%	$56.1698	$56.17	$56.15	$56.20
Purchase #5	$69.66	13.564%	$79.1087	$79.11	$79.10	$79.10
Purchase #6	$115.46	3.246%	$119.2078	$119.21	$119.20	$119.20
Purchase #7	$34.67	12.155%	$38.8841	$38.88	$38.90	$38.90
7 purchase totals =	$622.49		$660.7550	$660.75	$660.75	$660.80