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	$51.64	7.322%	$55.4211	$55.42	$55.40	$55.40
Purchase #2	$157.38	9.519%	$172.361	$172.36	$172.35	$172.40
Purchase #3	$118.36	12.201%	$132.8011	$132.80	$132.80	$132.80
Purchase #4	$59.81	9.704%	$65.614	$65.61	$65.60	$65.60
Purchase #5	$234.83	9.157%	$256.3334	$256.33	$256.35	$256.30
Purchase #6	$111.68	8.254%	$120.8981	$120.90	$120.90	$120.90
Purchase #7	$151.46	11.320%	$168.6053	$168.61	$168.60	$168.60
7 purchase totals =	$885.16		$972.0340	$972.03	$972.00	$972.00