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	$230.90	13.686%	$262.501	$262.50	$262.50	$262.50
Purchase #2	$39.99	13.124%	$45.2383	$45.24	$45.25	$45.20
Purchase #3	$176.51	4.629%	$184.6806	$184.68	$184.70	$184.70
Purchase #4	$101.86	10.765%	$112.8252	$112.83	$112.85	$112.80
Purchase #5	$160.52	3.263%	$165.7578	$165.76	$165.75	$165.80
Purchase #6	$231.90	10.333%	$255.8622	$255.86	$255.85	$255.90
Purchase #7	$209.31	6.827%	$223.5996	$223.60	$223.60	$223.60
7 purchase totals =	$1,150.99		$1,250.4647	$1,250.47	$1,250.50	$1,250.50