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	$136.86	12.766%	$154.3315	$154.33	$154.35	$154.30
Purchase #2	$96.75	12.667%	$109.0053	$109.01	$109.00	$109.00
Purchase #3	$183.92	6.632%	$196.1176	$196.12	$196.10	$196.10
Purchase #4	$224.82	9.730%	$246.695	$246.70	$246.70	$246.70
Purchase #5	$12.48	4.797%	$13.0787	$13.08	$13.10	$13.10
Purchase #6	$174.98	3.566%	$181.2198	$181.22	$181.20	$181.20
Purchase #7	$98.90	6.817%	$105.642	$105.64	$105.65	$105.60
7 purchase totals =	$928.71		$1,006.0899	$1,006.10	$1,006.10	$1,006.00