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	$18.25	3.556%	$18.899	$18.90	$18.90	$18.90
Purchase #2	$123.46	6.369%	$131.3232	$131.32	$131.30	$131.30
Purchase #3	$209.76	3.709%	$217.54	$217.54	$217.55	$217.50
Purchase #4	$241.40	4.576%	$252.4465	$252.45	$252.45	$252.40
Purchase #5	$171.90	9.724%	$188.6156	$188.62	$188.60	$188.60
Purchase #6	$46.72	3.223%	$48.2258	$48.23	$48.25	$48.20
Purchase #7	$60.76	13.113%	$68.7275	$68.73	$68.75	$68.70
7 purchase totals =	$872.25		$925.7776	$925.79	$925.80	$925.60