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	$40.76	8.637%	$44.2804	$44.28	$44.30	$44.30
Purchase #2	$141.90	9.550%	$155.4515	$155.45	$155.45	$155.50
Purchase #3	$80.46	11.475%	$89.6928	$89.69	$89.70	$89.70
Purchase #4	$221.60	13.501%	$251.5182	$251.52	$251.50	$251.50
Purchase #5	$59.47	4.169%	$61.9493	$61.95	$61.95	$61.90
Purchase #6	$161.35	6.215%	$171.3779	$171.38	$171.40	$171.40
Purchase #7	$200.60	12.708%	$226.0922	$226.09	$226.10	$226.10
7 purchase totals =	$906.14		$1,000.3623	$1,000.36	$1,000.40	$1,000.40