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	$127.53	9.168%	$139.222	$139.22	$139.20	$139.20
Purchase #2	$168.91	12.486%	$190.0001	$190.00	$190.00	$190.00
Purchase #3	$210.91	6.858%	$225.3742	$225.37	$225.35	$225.40
Purchase #4	$181.96	9.169%	$198.6439	$198.64	$198.65	$198.60
Purchase #5	$196.79	11.456%	$219.3343	$219.33	$219.35	$219.30
Purchase #6	$230.94	10.813%	$255.9115	$255.91	$255.90	$255.90
Purchase #7	$151.62	11.723%	$169.3944	$169.39	$169.40	$169.40
7 purchase totals =	$1,268.66		$1,397.8804	$1,397.86	$1,397.85	$1,397.80