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	$235.47	12.714%	$265.4077	$265.41	$265.40	$265.40
Purchase #2	$20.80	13.197%	$23.545	$23.55	$23.55	$23.50
Purchase #3	$48.82	8.722%	$53.0781	$53.08	$53.10	$53.10
Purchase #4	$20.66	3.753%	$21.4354	$21.44	$21.45	$21.40
Purchase #5	$151.70	3.219%	$156.5832	$156.58	$156.60	$156.60
Purchase #6	$176.76	11.165%	$196.4953	$196.50	$196.50	$196.50
Purchase #7	$136.69	3.372%	$141.2992	$141.30	$141.30	$141.30
7 purchase totals =	$790.90		$857.8439	$857.86	$857.90	$857.80