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	$96.53	12.592%	$108.6851	$108.69	$108.70	$108.70
Purchase #2	$66.51	9.640%	$72.9216	$72.92	$72.90	$72.90
Purchase #3	$220.27	4.182%	$229.4817	$229.48	$229.50	$229.50
Purchase #4	$208.46	8.649%	$226.4897	$226.49	$226.50	$226.50
Purchase #5	$46.77	11.141%	$51.9806	$51.98	$52.00	$52.00
Purchase #6	$41.52	12.123%	$46.5535	$46.55	$46.55	$46.60
Purchase #7	$126.84	12.387%	$142.5517	$142.55	$142.55	$142.60
7 purchase totals =	$806.90		$878.6639	$878.66	$878.70	$878.80