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	$7.44	10.305%	$8.2067	$8.21	$8.20	$8.20
Purchase #2	$55.80	8.556%	$60.5742	$60.57	$60.55	$60.60
Purchase #3	$50.88	10.305%	$56.1232	$56.12	$56.10	$56.10
Purchase #4	$43.80	3.504%	$45.3348	$45.33	$45.35	$45.30
Purchase #5	$129.71	11.673%	$144.851	$144.85	$144.85	$144.90
Purchase #6	$183.31	8.493%	$198.8785	$198.88	$198.90	$198.90
Purchase #7	$90.54	10.786%	$100.3056	$100.31	$100.30	$100.30
7 purchase totals =	$561.48		$614.2740	$614.27	$614.25	$614.30