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	$60.60	4.591%	$63.3821	$63.38	$63.40	$63.40
Purchase #2	$153.37	12.732%	$172.8971	$172.90	$172.90	$172.90
Purchase #3	$44.61	10.591%	$49.3346	$49.33	$49.35	$49.30
Purchase #4	$46.54	12.182%	$52.2095	$52.21	$52.20	$52.20
Purchase #5	$134.87	9.435%	$147.595	$147.60	$147.60	$147.60
Purchase #6	$6.90	4.288%	$7.1959	$7.20	$7.20	$7.20
Purchase #7	$85.47	11.825%	$95.5768	$95.58	$95.60	$95.60
7 purchase totals =	$532.36		$588.1910	$588.20	$588.25	$588.20