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	$77.91	7.139%	$83.472	$83.47	$83.45	$83.50
Purchase #2	$166.49	7.617%	$179.1715	$179.17	$179.15	$179.20
Purchase #3	$205.29	13.607%	$233.2238	$233.22	$233.20	$233.20
Purchase #4	$50.41	4.854%	$52.8569	$52.86	$52.85	$52.90
Purchase #5	$237.94	10.771%	$263.5685	$263.57	$263.55	$263.60
Purchase #6	$35.96	11.724%	$40.176	$40.18	$40.20	$40.20
Purchase #7	$116.51	13.751%	$132.5313	$132.53	$132.55	$132.50
7 purchase totals =	$890.51		$985.0000	$985.00	$984.95	$985.10