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	$250.72	7.680%	$269.9753	$269.98	$270.00	$270.00
Purchase #2	$101.95	7.726%	$109.8267	$109.83	$109.85	$109.80
Purchase #3	$67.52	6.326%	$71.7913	$71.79	$71.80	$71.80
Purchase #4	$92.56	8.410%	$100.3443	$100.34	$100.35	$100.30
Purchase #5	$57.45	9.402%	$62.8514	$62.85	$62.85	$62.90
Purchase #6	$185.25	10.304%	$204.3382	$204.34	$204.35	$204.30
Purchase #7	$45.58	8.401%	$49.4092	$49.41	$49.40	$49.40
7 purchase totals =	$801.03		$868.5364	$868.54	$868.60	$868.50