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	$20.38	4.724%	$21.3428	$21.34	$21.35	$21.30
Purchase #2	$221.87	9.567%	$243.0963	$243.10	$243.10	$243.10
Purchase #3	$175.43	10.158%	$193.2502	$193.25	$193.25	$193.30
Purchase #4	$149.91	8.653%	$162.8817	$162.88	$162.90	$162.90
Purchase #5	$13.53	5.196%	$14.233	$14.23	$14.25	$14.20
Purchase #6	$94.78	6.420%	$100.8649	$100.86	$100.85	$100.90
Purchase #7	$90.57	11.351%	$100.8506	$100.85	$100.85	$100.90
7 purchase totals =	$766.47		$836.5195	$836.51	$836.55	$836.60