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	$43.61	13.800%	$49.6282	$49.63	$49.65	$49.60
Purchase #2	$161.94	6.757%	$172.8823	$172.88	$172.90	$172.90
Purchase #3	$17.86	3.449%	$18.476	$18.48	$18.50	$18.50
Purchase #4	$79.71	12.443%	$89.6283	$89.63	$89.65	$89.60
Purchase #5	$133.61	3.745%	$138.6137	$138.61	$138.60	$138.60
Purchase #6	$110.75	9.455%	$121.2214	$121.22	$121.20	$121.20
Purchase #7	$10.46	9.302%	$11.433	$11.43	$11.45	$11.40
7 purchase totals =	$557.94		$601.8829	$601.88	$601.95	$601.80