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	$218.79	3.678%	$226.8371	$226.84	$226.85	$226.80
Purchase #2	$93.45	12.271%	$104.9172	$104.92	$104.90	$104.90
Purchase #3	$133.77	10.275%	$147.5149	$147.51	$147.50	$147.50
Purchase #4	$30.85	13.659%	$35.0638	$35.06	$35.05	$35.10
Purchase #5	$11.32	11.359%	$12.6058	$12.61	$12.60	$12.60
Purchase #6	$82.26	11.382%	$91.6228	$91.62	$91.60	$91.60
Purchase #7	$62.50	6.546%	$66.5913	$66.59	$66.60	$66.60
7 purchase totals =	$632.94		$685.1529	$685.15	$685.10	$685.10