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	$235.89	9.865%	$259.1605	$259.16	$259.15	$259.20
Purchase #2	$55.78	12.227%	$62.6002	$62.60	$62.60	$62.60
Purchase #3	$41.77	7.398%	$44.8601	$44.86	$44.85	$44.90
Purchase #4	$48.42	3.470%	$50.1002	$50.10	$50.10	$50.10
Purchase #5	$82.25	3.742%	$85.3278	$85.33	$85.35	$85.30
Purchase #6	$114.32	8.323%	$123.8349	$123.83	$123.85	$123.80
Purchase #7	$66.94	8.194%	$72.4251	$72.43	$72.45	$72.40
7 purchase totals =	$645.37		$698.3088	$698.31	$698.35	$698.30