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	$151.48	13.243%	$171.5405	$171.54	$171.55	$171.50
Purchase #2	$209.97	7.176%	$225.0374	$225.04	$225.05	$225.00
Purchase #3	$31.83	6.358%	$33.8538	$33.85	$33.85	$33.90
Purchase #4	$81.51	10.153%	$89.7857	$89.79	$89.80	$89.80
Purchase #5	$32.55	6.824%	$34.7712	$34.77	$34.75	$34.80
Purchase #6	$65.59	10.278%	$72.3313	$72.33	$72.35	$72.30
Purchase #7	$162.69	8.655%	$176.7708	$176.77	$176.75	$176.80
7 purchase totals =	$735.62		$804.0907	$804.09	$804.10	$804.10