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	$29.82	4.221%	$31.0787	$31.08	$31.10	$31.10
Purchase #2	$71.25	10.117%	$78.4584	$78.46	$78.45	$78.50
Purchase #3	$96.32	7.344%	$103.3937	$103.39	$103.40	$103.40
Purchase #4	$71.95	7.494%	$77.3419	$77.34	$77.35	$77.30
Purchase #5	$39.89	11.381%	$44.4299	$44.43	$44.45	$44.40
Purchase #6	$99.25	3.296%	$102.5213	$102.52	$102.50	$102.50
Purchase #7	$168.59	12.381%	$189.4631	$189.46	$189.45	$189.50
7 purchase totals =	$577.07		$626.6870	$626.68	$626.70	$626.70