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	$98.63	10.686%	$109.1696	$109.17	$109.15	$109.20
Purchase #2	$233.97	13.632%	$265.8648	$265.86	$265.85	$265.90
Purchase #3	$224.76	13.820%	$255.8218	$255.82	$255.80	$255.80
Purchase #4	$142.71	9.610%	$156.4244	$156.42	$156.40	$156.40
Purchase #5	$74.58	3.815%	$77.4252	$77.43	$77.45	$77.40
Purchase #6	$228.92	8.506%	$248.3919	$248.39	$248.40	$248.40
Purchase #7	$229.78	3.656%	$238.1808	$238.18	$238.20	$238.20
7 purchase totals =	$1,233.35		$1,351.2785	$1,351.27	$1,351.25	$1,351.30