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	$29.72	5.696%	$31.4129	$31.41	$31.40	$31.40
Purchase #2	$61.42	9.698%	$67.3765	$67.38	$67.40	$67.40
Purchase #3	$203.78	5.259%	$214.4968	$214.50	$214.50	$214.50
Purchase #4	$96.68	4.862%	$101.3806	$101.38	$101.40	$101.40
Purchase #5	$198.52	5.206%	$208.855	$208.86	$208.85	$208.90
Purchase #6	$39.30	11.418%	$43.7873	$43.79	$43.80	$43.80
Purchase #7	$177.92	6.827%	$190.0666	$190.07	$190.05	$190.10
7 purchase totals =	$807.34		$857.3757	$857.39	$857.40	$857.50