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	$200.37	10.718%	$221.8457	$221.85	$221.85	$221.80
Purchase #2	$92.37	3.401%	$95.5115	$95.51	$95.50	$95.50
Purchase #3	$205.87	13.502%	$233.6666	$233.67	$233.65	$233.70
Purchase #4	$233.75	10.508%	$258.3125	$258.31	$258.30	$258.30
Purchase #5	$7.48	5.738%	$7.9092	$7.91	$7.90	$7.90
Purchase #6	$74.32	8.758%	$80.8289	$80.83	$80.85	$80.80
Purchase #7	$77.61	6.458%	$82.6221	$82.62	$82.60	$82.60
7 purchase totals =	$891.77		$980.6965	$980.70	$980.65	$980.60