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	$78.52	5.583%	$82.9038	$82.90	$82.90	$82.90
Purchase #2	$139.57	4.873%	$146.3712	$146.37	$146.35	$146.40
Purchase #3	$140.95	6.773%	$150.4965	$150.50	$150.50	$150.50
Purchase #4	$21.67	10.614%	$23.9701	$23.97	$23.95	$24.00
Purchase #5	$84.40	4.283%	$88.0149	$88.01	$88.00	$88.00
Purchase #6	$99.38	12.538%	$111.8403	$111.84	$111.85	$111.80
Purchase #7	$55.31	10.418%	$61.0722	$61.07	$61.05	$61.10
7 purchase totals =	$619.80		$664.6690	$664.66	$664.60	$664.70