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	$134.93	6.414%	$143.5844	$143.58	$143.60	$143.60
Purchase #2	$128.96	12.679%	$145.3108	$145.31	$145.30	$145.30
Purchase #3	$192.84	11.115%	$214.2742	$214.27	$214.25	$214.30
Purchase #4	$114.43	11.788%	$127.919	$127.92	$127.90	$127.90
Purchase #5	$124.67	6.159%	$132.3484	$132.35	$132.35	$132.30
Purchase #6	$7.53	8.242%	$8.1506	$8.15	$8.15	$8.20
Purchase #7	$110.89	7.589%	$119.3054	$119.31	$119.30	$119.30
7 purchase totals =	$814.25		$890.8928	$890.89	$890.85	$890.90