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	$74.56	5.210%	$78.4446	$78.44	$78.45	$78.40
Purchase #2	$13.88	4.383%	$14.4884	$14.49	$14.50	$14.50
Purchase #3	$18.64	6.389%	$19.8309	$19.83	$19.85	$19.80
Purchase #4	$166.84	6.837%	$178.2469	$178.25	$178.25	$178.20
Purchase #5	$79.42	10.715%	$87.9299	$87.93	$87.95	$87.90
Purchase #6	$71.28	11.158%	$79.2334	$79.23	$79.25	$79.20
Purchase #7	$38.71	11.384%	$43.1167	$43.12	$43.10	$43.10
7 purchase totals =	$463.33		$501.2908	$501.29	$501.35	$501.10