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	$156.99	12.413%	$176.4772	$176.48	$176.50	$176.50
Purchase #2	$30.30	5.275%	$31.8983	$31.90	$31.90	$31.90
Purchase #3	$74.56	10.698%	$82.5364	$82.54	$82.55	$82.50
Purchase #4	$206.31	10.771%	$228.5317	$228.53	$228.55	$228.50
Purchase #5	$179.89	11.200%	$200.0377	$200.04	$200.05	$200.00
Purchase #6	$103.56	9.172%	$113.0585	$113.06	$113.05	$113.10
Purchase #7	$46.37	5.682%	$49.0047	$49.00	$49.00	$49.00
7 purchase totals =	$797.98		$881.5445	$881.55	$881.60	$881.50