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	$27.33	11.297%	$30.4175	$30.42	$30.40	$30.40
Purchase #2	$51.79	9.410%	$56.6634	$56.66	$56.65	$56.70
Purchase #3	$205.81	11.221%	$228.9039	$228.90	$228.90	$228.90
Purchase #4	$155.38	4.308%	$162.0738	$162.07	$162.05	$162.10
Purchase #5	$18.58	12.262%	$20.8583	$20.86	$20.85	$20.90
Purchase #6	$118.96	6.837%	$127.0933	$127.09	$127.10	$127.10
Purchase #7	$174.44	12.596%	$196.4125	$196.41	$196.40	$196.40
7 purchase totals =	$752.29		$822.4227	$822.41	$822.35	$822.50