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	$26.50	9.689%	$29.0676	$29.07	$29.05	$29.10
Purchase #2	$181.70	7.208%	$194.7969	$194.80	$194.80	$194.80
Purchase #3	$186.57	7.444%	$200.4583	$200.46	$200.45	$200.50
Purchase #4	$59.75	11.794%	$66.7969	$66.80	$66.80	$66.80
Purchase #5	$164.53	9.708%	$180.5026	$180.50	$180.50	$180.50
Purchase #6	$99.82	11.423%	$111.2224	$111.22	$111.20	$111.20
Purchase #7	$47.84	12.291%	$53.72	$53.72	$53.70	$53.70
7 purchase totals =	$766.71		$836.5647	$836.57	$836.50	$836.60