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	$80.35	3.420%	$83.098	$83.10	$83.10	$83.10
Purchase #2	$178.45	4.709%	$186.8532	$186.85	$186.85	$186.90
Purchase #3	$34.43	5.563%	$36.3453	$36.35	$36.35	$36.30
Purchase #4	$49.85	6.680%	$53.18	$53.18	$53.20	$53.20
Purchase #5	$52.61	8.603%	$57.136	$57.14	$57.15	$57.10
Purchase #6	$146.96	11.738%	$164.2102	$164.21	$164.20	$164.20
Purchase #7	$100.53	11.839%	$112.4317	$112.43	$112.45	$112.40
7 purchase totals =	$643.18		$693.2544	$693.26	$693.30	$693.20