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	$225.40	6.149%	$239.2598	$239.26	$239.25	$239.30
Purchase #2	$101.66	12.655%	$114.5251	$114.53	$114.55	$114.50
Purchase #3	$142.79	5.433%	$150.5478	$150.55	$150.55	$150.50
Purchase #4	$45.86	12.811%	$51.7351	$51.74	$51.75	$51.70
Purchase #5	$28.92	8.685%	$31.4317	$31.43	$31.45	$31.40
Purchase #6	$81.79	9.815%	$89.8177	$89.82	$89.80	$89.80
Purchase #7	$226.89	4.820%	$237.8261	$237.83	$237.85	$237.80
7 purchase totals =	$853.31		$915.1433	$915.16	$915.20	$915.00