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	$160.86	4.772%	$168.5362	$168.54	$168.55	$168.50
Purchase #2	$169.50	11.840%	$189.5688	$189.57	$189.55	$189.60
Purchase #3	$30.42	7.485%	$32.6969	$32.70	$32.70	$32.70
Purchase #4	$202.46	13.383%	$229.5552	$229.56	$229.55	$229.60
Purchase #5	$119.70	10.772%	$132.5941	$132.59	$132.60	$132.60
Purchase #6	$17.97	11.323%	$20.0047	$20.00	$20.00	$20.00
Purchase #7	$74.45	10.226%	$82.0633	$82.06	$82.05	$82.10
7 purchase totals =	$775.36		$855.0192	$855.02	$855.00	$855.10