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	$226.74	12.752%	$255.6539	$255.65	$255.65	$255.70
Purchase #2	$73.94	13.448%	$83.8835	$83.88	$83.90	$83.90
Purchase #3	$33.84	11.824%	$37.8412	$37.84	$37.85	$37.80
Purchase #4	$146.51	5.420%	$154.4508	$154.45	$154.45	$154.50
Purchase #5	$98.58	7.320%	$105.7961	$105.80	$105.80	$105.80
Purchase #6	$104.69	3.625%	$108.485	$108.49	$108.50	$108.50
Purchase #7	$101.79	11.108%	$113.0968	$113.10	$113.10	$113.10
7 purchase totals =	$786.09		$859.2073	$859.21	$859.25	$859.30