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	$88.74	12.221%	$99.5849	$99.58	$99.60	$99.60
Purchase #2	$170.71	9.785%	$187.414	$187.41	$187.40	$187.40
Purchase #3	$9.88	4.730%	$10.3473	$10.35	$10.35	$10.30
Purchase #4	$123.41	3.514%	$127.7466	$127.75	$127.75	$127.70
Purchase #5	$116.25	3.451%	$120.2618	$120.26	$120.25	$120.30
Purchase #6	$80.84	5.672%	$85.4252	$85.43	$85.45	$85.40
Purchase #7	$196.72	9.476%	$215.3612	$215.36	$215.35	$215.40
7 purchase totals =	$786.55		$846.1410	$846.14	$846.15	$846.10