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	$31.72	6.525%	$33.7897	$33.79	$33.80	$33.80
Purchase #2	$56.59	4.560%	$59.1705	$59.17	$59.15	$59.20
Purchase #3	$13.50	9.502%	$14.7828	$14.78	$14.80	$14.80
Purchase #4	$242.96	9.509%	$266.0631	$266.06	$266.05	$266.10
Purchase #5	$214.77	8.543%	$233.1178	$233.12	$233.10	$233.10
Purchase #6	$34.85	3.124%	$35.9387	$35.94	$35.95	$35.90
Purchase #7	$35.58	8.150%	$38.4798	$38.48	$38.50	$38.50
7 purchase totals =	$629.97		$681.3424	$681.34	$681.35	$681.40