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	$165.30	9.225%	$180.5489	$180.55	$180.55	$180.50
Purchase #2	$62.57	11.719%	$69.9026	$69.90	$69.90	$69.90
Purchase #3	$85.45	5.624%	$90.2557	$90.26	$90.25	$90.30
Purchase #4	$75.39	6.310%	$80.1471	$80.15	$80.15	$80.10
Purchase #5	$246.29	5.535%	$259.9222	$259.92	$259.90	$259.90
Purchase #6	$29.92	4.509%	$31.2691	$31.27	$31.25	$31.30
Purchase #7	$198.93	5.789%	$210.4461	$210.45	$210.45	$210.40
7 purchase totals =	$863.85		$922.4917	$922.50	$922.45	$922.40