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	$99.69	12.441%	$112.0924	$112.09	$112.10	$112.10
Purchase #2	$248.48	3.365%	$256.8414	$256.84	$256.85	$256.80
Purchase #3	$55.53	10.831%	$61.5445	$61.54	$61.55	$61.50
Purchase #4	$181.92	9.624%	$199.428	$199.43	$199.45	$199.40
Purchase #5	$9.60	6.686%	$10.2419	$10.24	$10.25	$10.20
Purchase #6	$54.89	11.717%	$61.3215	$61.32	$61.30	$61.30
Purchase #7	$206.55	3.830%	$214.4609	$214.46	$214.45	$214.50
7 purchase totals =	$856.66		$915.9306	$915.92	$915.95	$915.80