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	$125.33	12.169%	$140.5814	$140.58	$140.60	$140.60
Purchase #2	$148.38	4.814%	$155.523	$155.52	$155.50	$155.50
Purchase #3	$233.32	9.515%	$255.5204	$255.52	$255.50	$255.50
Purchase #4	$144.39	9.807%	$158.5503	$158.55	$158.55	$158.60
Purchase #5	$140.39	4.565%	$146.7988	$146.80	$146.80	$146.80
Purchase #6	$148.64	13.830%	$169.1969	$169.20	$169.20	$169.20
Purchase #7	$9.79	9.228%	$10.6934	$10.69	$10.70	$10.70
7 purchase totals =	$950.24		$1,036.8642	$1,036.86	$1,036.85	$1,036.90