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	$84.48	8.724%	$91.85	$91.85	$91.85	$91.90
Purchase #2	$103.51	4.586%	$108.257	$108.26	$108.25	$108.30
Purchase #3	$99.87	3.527%	$103.3924	$103.39	$103.40	$103.40
Purchase #4	$79.30	13.416%	$89.9389	$89.94	$89.95	$89.90
Purchase #5	$142.33	10.317%	$157.0142	$157.01	$157.00	$157.00
Purchase #6	$72.99	6.731%	$77.903	$77.90	$77.90	$77.90
Purchase #7	$50.70	10.710%	$56.13	$56.13	$56.15	$56.10
7 purchase totals =	$633.18		$684.4855	$684.48	$684.50	$684.50