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	$48.69	13.166%	$55.1005	$55.10	$55.10	$55.10
Purchase #2	$103.77	5.181%	$109.1463	$109.15	$109.15	$109.10
Purchase #3	$27.30	9.863%	$29.9926	$29.99	$30.00	$30.00
Purchase #4	$48.38	7.684%	$52.0975	$52.10	$52.10	$52.10
Purchase #5	$11.86	5.411%	$12.5017	$12.50	$12.50	$12.50
Purchase #6	$38.53	7.311%	$41.3469	$41.35	$41.35	$41.30
Purchase #7	$179.88	10.113%	$198.0713	$198.07	$198.05	$198.10
7 purchase totals =	$458.41		$498.2568	$498.26	$498.25	$498.20