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	$155.37	8.587%	$168.7116	$168.71	$168.70	$168.70
Purchase #2	$128.72	10.798%	$142.6192	$142.62	$142.60	$142.60
Purchase #3	$169.66	12.438%	$190.7623	$190.76	$190.75	$190.80
Purchase #4	$49.40	13.823%	$56.2286	$56.23	$56.25	$56.20
Purchase #5	$102.33	9.517%	$112.0687	$112.07	$112.05	$112.10
Purchase #6	$18.86	9.255%	$20.6055	$20.61	$20.60	$20.60
Purchase #7	$248.91	4.270%	$259.5385	$259.54	$259.55	$259.50
7 purchase totals =	$873.25		$950.5344	$950.54	$950.50	$950.50