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	$28.52	11.805%	$31.8868	$31.89	$31.90	$31.90
Purchase #2	$190.75	4.115%	$198.5994	$198.60	$198.60	$198.60
Purchase #3	$226.52	9.154%	$247.2556	$247.26	$247.25	$247.30
Purchase #4	$124.26	3.429%	$128.5209	$128.52	$128.50	$128.50
Purchase #5	$171.43	3.751%	$177.8603	$177.86	$177.85	$177.90
Purchase #6	$105.40	13.544%	$119.6754	$119.68	$119.70	$119.70
Purchase #7	$139.52	9.351%	$152.5665	$152.57	$152.55	$152.60
7 purchase totals =	$986.40		$1,056.3649	$1,056.38	$1,056.35	$1,056.50