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	$30.90	4.786%	$32.3789	$32.38	$32.40	$32.40
Purchase #2	$115.35	7.226%	$123.6852	$123.69	$123.70	$123.70
Purchase #3	$68.93	7.215%	$73.9033	$73.90	$73.90	$73.90
Purchase #4	$197.72	12.855%	$223.1369	$223.14	$223.15	$223.10
Purchase #5	$184.30	9.331%	$201.497	$201.50	$201.50	$201.50
Purchase #6	$101.91	9.235%	$111.3214	$111.32	$111.30	$111.30
Purchase #7	$131.72	8.468%	$142.874	$142.87	$142.85	$142.90
7 purchase totals =	$830.83		$908.7967	$908.80	$908.80	$908.80