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	$125.97	6.260%	$133.8557	$133.86	$133.85	$133.90
Purchase #2	$123.45	5.822%	$130.6373	$130.64	$130.65	$130.60
Purchase #3	$127.25	9.650%	$139.5296	$139.53	$139.55	$139.50
Purchase #4	$124.92	6.469%	$133.0011	$133.00	$133.00	$133.00
Purchase #5	$41.99	3.321%	$43.3845	$43.38	$43.40	$43.40
Purchase #6	$26.83	8.455%	$29.0985	$29.10	$29.10	$29.10
Purchase #7	$52.31	13.726%	$59.4901	$59.49	$59.50	$59.50
7 purchase totals =	$622.72		$668.9968	$669.00	$669.05	$669.00