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	$123.25	4.509%	$128.8073	$128.81	$128.80	$128.80
Purchase #2	$249.55	5.594%	$263.5098	$263.51	$263.50	$263.50
Purchase #3	$164.47	4.392%	$171.6935	$171.69	$171.70	$171.70
Purchase #4	$247.85	11.105%	$275.3737	$275.37	$275.35	$275.40
Purchase #5	$86.58	11.851%	$96.8406	$96.84	$96.85	$96.80
Purchase #6	$155.52	7.407%	$167.0394	$167.04	$167.05	$167.00
Purchase #7	$65.72	13.828%	$74.8078	$74.81	$74.80	$74.80
7 purchase totals =	$1,092.94		$1,178.0721	$1,178.07	$1,178.05	$1,178.00