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	$88.61	12.500%	$99.6863	$99.69	$99.70	$99.70
Purchase #2	$156.40	5.202%	$164.5359	$164.54	$164.55	$164.50
Purchase #3	$53.83	13.558%	$61.1283	$61.13	$61.15	$61.10
Purchase #4	$61.46	11.568%	$68.5697	$68.57	$68.55	$68.60
Purchase #5	$27.67	13.654%	$31.4481	$31.45	$31.45	$31.40
Purchase #6	$131.35	5.385%	$138.4232	$138.42	$138.40	$138.40
Purchase #7	$61.85	8.277%	$66.9693	$66.97	$66.95	$67.00
7 purchase totals =	$581.17		$630.7608	$630.77	$630.75	$630.70