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	$231.43	9.272%	$252.8882	$252.89	$252.90	$252.90
Purchase #2	$183.51	9.220%	$200.4296	$200.43	$200.45	$200.40
Purchase #3	$238.55	8.706%	$259.3182	$259.32	$259.30	$259.30
Purchase #4	$210.26	12.372%	$236.2734	$236.27	$236.25	$236.30
Purchase #5	$55.48	7.388%	$59.5789	$59.58	$59.60	$59.60
Purchase #6	$172.91	7.474%	$185.8333	$185.83	$185.85	$185.80
Purchase #7	$102.94	8.593%	$111.7856	$111.79	$111.80	$111.80
7 purchase totals =	$1,195.08		$1,306.1072	$1,306.11	$1,306.15	$1,306.10